diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index d33d1ee..82b9cd0 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -24,7 +24,7 @@
 use Symfony\Component\DependencyInjection\Exception\RuntimeException as DependencyInjectionRuntimeException;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Lock\DatabaseLockBackend;
 use Drupal\Core\Lock\LockBackendInterface;
 use Drupal\Core\Session\AnonymousUserSession;
@@ -1844,7 +1844,7 @@ function drupal_installation_attempted() {
  * @see \Drupal\Core\Language\LanguageManager
  *
  * @param string $type
- *   The type of language object needed, e.g. Language::TYPE_INTERFACE.
+ *   The type of language object needed, e.g. LanguageInterface::TYPE_INTERFACE.
  *
  * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
  *   Use \Drupal::languageManager()->getCurrentLanguage().
@@ -1858,17 +1858,17 @@ function language($type) {
  *
  * @param $flags
  *   (optional) Specifies the state of the languages that have to be returned.
- *   It can be: Language::STATE_CONFIGURABLE, Language::STATE_LOCKED,
- *   Language::STATE_ALL.
+ *   It can be: LanguageInterface::STATE_CONFIGURABLE,
+ *   LanguageInterface::STATE_LOCKED, or LanguageInterface::STATE_ALL.
  *
- * @return array
+ * @return \Drupal\Core\Language\LanguageInterface[]
  *   An associative array of languages, keyed by the language code, ordered by
  *   weight ascending and name ascending.
  *
  * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
  *   Use \Drupal::languageManager()->getLanguages().
  */
-function language_list($flags = Language::STATE_CONFIGURABLE) {
+function language_list($flags = LanguageInterface::STATE_CONFIGURABLE) {
   return \Drupal::languageManager()->getLanguages($flags);
 }
 
diff --git a/core/includes/common.inc b/core/includes/common.inc
index f30bcdf..f4d6147 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -18,7 +18,7 @@
 use Drupal\Component\Utility\Tags;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Site\Settings;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpFoundation\Request;
@@ -414,7 +414,7 @@ function check_url($uri) {
  * Arbitrary elements may be added using the $args associative array.
  */
 function format_rss_channel($title, $link, $description, $items, $langcode = NULL, $args = array()) {
-  $langcode = $langcode ? $langcode : \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT)->id;
+  $langcode = $langcode ? $langcode : \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();
 
   $output = "<channel>\n";
   $output .= ' <title>' . String::checkPlain($title) . "</title>\n";
@@ -875,7 +875,7 @@ function l($text, $path, array $options = array()) {
   // Add a hreflang attribute if we know the language of this link's url and
   // hreflang has not already been set.
   if (!empty($variables['options']['language']) && !isset($variables['options']['attributes']['hreflang'])) {
-    $variables['options']['attributes']['hreflang'] = $variables['options']['language']->id;
+    $variables['options']['attributes']['hreflang'] = $variables['options']['language']->getId();
   }
 
   // Set the "active" class if the 'set_active_class' option is not empty.
@@ -1801,7 +1801,7 @@ function _drupal_add_js($data = NULL, $options = NULL) {
             'currentPath' => $current_path,
             'currentPathIsAdmin' => $current_path_is_admin,
             'isFront' => drupal_is_front_page(),
-            'currentLanguage' => \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_URL)->id,
+            'currentLanguage' => \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_URL)->getId(),
           );
           if (!empty($current_query)) {
             ksort($current_query);
diff --git a/core/includes/entity.inc b/core/includes/entity.inc
index b28132b..95e0fca 100644
--- a/core/includes/entity.inc
+++ b/core/includes/entity.inc
@@ -8,7 +8,6 @@
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\EntityStorageException;
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
 
 /**
  * Resets the cached information about entity types.
diff --git a/core/includes/form.inc b/core/includes/form.inc
index 42206a4..43ae137 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -12,7 +12,6 @@
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Database\Database;
 use Drupal\Core\Form\OptGroup;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Template\Attribute;
 use Drupal\Core\Utility\Color;
@@ -2027,7 +2026,7 @@ function form_process_machine_name($element, &$form_state) {
       'machineName' => array(
         '#' . $source['#id'] => $element['#machine_name'],
       ),
-      'langcode' => $language->id,
+      'langcode' => $language->getId(),
     ),
   );
   $element['#attached']['library'][] = 'core/drupal.machine-name';
diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 0fefe74..9364146 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -7,7 +7,6 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Template\Attribute;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index e44f13d..30aaf33 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -13,7 +13,6 @@
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Config\Config;
 use Drupal\Core\Config\StorageException;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Extension\Extension;
 use Drupal\Core\Extension\ExtensionNameLengthException;
 use Drupal\Core\Page\FeedLinkElement;
@@ -1213,7 +1212,7 @@ function template_preprocess_links(&$variables) {
           $link_element['#options']['set_active_class'] = TRUE;
 
           if (!empty($link['language'])) {
-            $li_attributes['hreflang'] = $link['language']->id;
+            $li_attributes['hreflang'] = $link['language']->getId();
           }
 
           // Add a "data-drupal-link-query" attribute to let the
@@ -2098,7 +2097,7 @@ function template_preprocess_page(&$variables) {
   $variables['base_path']         = base_path();
   $variables['front_page']        = url();
   $variables['language']          = $language_interface;
-  $variables['language']->dir     = $language_interface->direction ? 'rtl' : 'ltr';
+  $variables['language']->dir     = $language_interface->getDirection() ? 'rtl' : 'ltr';
   $variables['logo']              = theme_get_setting('logo.url');
   $variables['site_name']         = (theme_get_setting('features.name') ? String::checkPlain($site_config->get('name')) : '');
   $variables['site_slogan']       = (theme_get_setting('features.slogan') ? Xss::filterAdmin($site_config->get('slogan')) : '');
diff --git a/core/includes/update.inc b/core/includes/update.inc
index 694a8a9..b54f572 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -13,6 +13,8 @@
 use Drupal\Core\Config\FileStorage;
 use Drupal\Core\Config\ConfigException;
 use Drupal\Core\DrupalKernel;
+use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Page\DefaultHtmlPageRenderer;
 use Drupal\Core\Utility\Error;
 use Drupal\Component\Uuid\Uuid;
@@ -800,14 +802,14 @@ function update_replace_permissions($replace) {
  *
  * @param $flags
  *   (optional) Specifies the state of the languages that have to be returned.
- *   It can be: Language::STATE_CONFIGURABLE, Language::STATE_LOCKED,
- *   Language::STATE_ALL.
+ *   It can be: LanguageInterface::STATE_CONFIGURABLE, LanguageInterface::STATE_LOCKED,
+ *   LanguageInterface::STATE_ALL.
  *
  * @return array
  *   An associative array of languages, keyed by the language code, ordered by
  *   weight ascending and name ascending.
  */
-function update_language_list($flags = Language::STATE_CONFIGURABLE) {
+function update_language_list($flags = LanguageInterface::STATE_CONFIGURABLE) {
 
   $languages = &drupal_static(__FUNCTION__);
 
@@ -829,7 +831,7 @@ function update_language_list($flags = Language::STATE_CONFIGURABLE) {
         $langcode = substr($langcode_config_name, strlen('language.entity.'));
         $info = \Drupal::config($langcode_config_name)->get();
         $languages[$langcode] = new Language(array(
-          'default' => ($info['id'] == $default->id),
+          'default' => ($info['id'] == $default->getId()),
           'name' => $info['label'],
           'id' => $info['id'],
           'direction' => $info['direction'],
@@ -837,13 +839,13 @@ function update_language_list($flags = Language::STATE_CONFIGURABLE) {
           'weight' => $info['weight'],
         ));
       }
-      Language::sort($languages);
+      uasort($languages, '\Drupal\Core\Language\Language::sort');
     }
     else {
       // No language module, so use the default language only.
-      $languages = array($default->id => $default);
+      $languages = array($default->getId() => $default);
       // Add the special languages, they will be filtered later if needed.
-      $languages += \Drupal::languageManager()->getDefaultLockedLanguages($default->weight);
+      $languages += \Drupal::languageManager()->getDefaultLockedLanguages($default->getWeight());
     }
   }
 
@@ -853,7 +855,7 @@ function update_language_list($flags = Language::STATE_CONFIGURABLE) {
   $filtered_languages = array();
 
   // Add the site's default language if flagged as allowed value.
-  if ($flags & Language::STATE_SITE_DEFAULT) {
+  if ($flags & LanguageInterface::STATE_SITE_DEFAULT) {
     $default = isset($default) ? $default : \Drupal::languageManager()->getDefaultLanguage();
     // Rename the default language.
     $default->name = t("Site's default language (@lang_name)", array('@lang_name' => $default->name));
@@ -861,7 +863,7 @@ function update_language_list($flags = Language::STATE_CONFIGURABLE) {
   }
 
   foreach ($languages as $langcode => $language) {
-    if (($language->locked && !($flags & Language::STATE_LOCKED)) || (!$language->locked && !($flags & Language::STATE_CONFIGURABLE))) {
+    if (($language->isLocked() && !($flags & LanguageInterface::STATE_LOCKED)) || (!$language->isLocked() && !($flags & LanguageInterface::STATE_CONFIGURABLE))) {
       continue;
      }
     $filtered_languages[$langcode] = $language;
diff --git a/core/lib/Drupal.php b/core/lib/Drupal.php
index 5c72435..6ea0bd0 100644
--- a/core/lib/Drupal.php
+++ b/core/lib/Drupal.php
@@ -461,7 +461,7 @@ public static function urlGenerator() {
    *     displayed outside the site, such as in an RSS feed.
    *   - 'language': An optional language object used to look up the alias
    *     for the URL. If $options['language'] is omitted, the language will be
-   *     obtained from \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_URL).
+   *     obtained from \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_URL).
    *   - 'https': Whether this URL should point to a secure location. If not
    *     defined, the current scheme is used, so the user stays on HTTP or HTTPS
    *     respectively. if mixed mode sessions are permitted, TRUE enforces HTTPS
diff --git a/core/lib/Drupal/Core/Cache/LanguageCacheContext.php b/core/lib/Drupal/Core/Cache/LanguageCacheContext.php
index e2c1bd9..0a3f16c 100644
--- a/core/lib/Drupal/Core/Cache/LanguageCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/LanguageCacheContext.php
@@ -45,7 +45,7 @@ public function getContext() {
     $context_parts = array();
     if ($this->languageManager->isMultilingual()) {
       foreach ($this->languageManager->getLanguageTypes() as $type) {
-        $context_parts[] = $this->languageManager->getCurrentLanguage($type)->id;
+        $context_parts[] = $this->languageManager->getCurrentLanguage($type)->getId();
       }
     }
     return implode(':', $context_parts);
diff --git a/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php b/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php
index 55eb6f6..3ea3dd4 100644
--- a/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php
+++ b/core/lib/Drupal/Core/Config/ConfigFactoryInterface.php
@@ -7,9 +7,6 @@
 
 namespace Drupal\Core\Config;
 
-use Drupal\Core\Language\Language;
-use Drupal\Core\Language\LanguageDefault;
-
 /**
  * Defines the interface for a configuration object factory.
  */
diff --git a/core/lib/Drupal/Core/Config/ConfigModuleOverridesEvent.php b/core/lib/Drupal/Core/Config/ConfigModuleOverridesEvent.php
index 26692ea..ced4228 100644
--- a/core/lib/Drupal/Core/Config/ConfigModuleOverridesEvent.php
+++ b/core/lib/Drupal/Core/Config/ConfigModuleOverridesEvent.php
@@ -8,7 +8,7 @@
 namespace Drupal\Core\Config;
 
 use Drupal\Component\Utility\NestedArray;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\EventDispatcher\Event;
 
 /**
@@ -42,10 +42,10 @@ class ConfigModuleOverridesEvent extends Event {
    *
    * @param array $names
    *   A list of configuration names.
-   * @param \Drupal\Core\Language\Language
+   * @param \Drupal\Core\Language\LanguageInterface
    *   (optional) The language for this configuration.
    */
-  public function __construct(array $names, Language $language = NULL) {
+  public function __construct(array $names, LanguageInterface $language = NULL) {
     $this->names = $names;
     $this->language = $language;
     $this->overrides = array();
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index 948ec6f..914e635 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -13,8 +13,8 @@
 use Drupal\Core\Entity\Entity;
 use Drupal\Core\Config\ConfigDuplicateUUIDException;
 use Drupal\Core\Entity\EntityStorageInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Plugin\PluginDependencyTrait;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Defines a base configuration entity class.
@@ -82,7 +82,7 @@
    *
    * @var string
    */
-  public $langcode = Language::LANGCODE_NOT_SPECIFIED;
+  public $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
 
   /**
    * Overrides Entity::__construct().
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
index 586d6df..baae80b 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityInterface.php
@@ -109,7 +109,7 @@ public function isSyncing();
    * entity change is part of an uninstall process, and skip executing your code
    * if that is the case.
    *
-   * For example, \Drupal\language\Entity\Language::preDelete() prevents the API
+   * For example, \Drupal\language\Entity\LanguageInterface::preDelete() prevents the API
    * from deleting the default language. However during an uninstall of the
    * language module it is expected that the default language should be deleted.
    *
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
index d23341b..cec215d 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php
@@ -183,7 +183,7 @@ protected function doLoadMultiple(array $ids = NULL) {
    */
   protected function doCreate(array $values) {
     // Set default language to site default if not provided.
-    $values += array('langcode' => $this->languageManager->getDefaultLanguage()->id);
+    $values += array('langcode' => $this->languageManager->getDefaultLanguage()->getId());
     $entity = new $this->entityClass($values, $this->entityTypeId);
 
     // Default status to enabled.
diff --git a/core/lib/Drupal/Core/Datetime/Date.php b/core/lib/Drupal/Core/Datetime/Date.php
index 2dd512a..d141042 100644
--- a/core/lib/Drupal/Core/Datetime/Date.php
+++ b/core/lib/Drupal/Core/Datetime/Date.php
@@ -132,7 +132,7 @@ public function format($timestamp, $type = 'medium', $format = '', $timezone = N
     }
 
     if (empty($langcode)) {
-      $langcode = $this->languageManager->getCurrentLanguage()->id;
+      $langcode = $this->languageManager->getCurrentLanguage()->getId();
     }
 
     // Create a DrupalDateTime object from the timestamp and timezone.
diff --git a/core/lib/Drupal/Core/Datetime/DrupalDateTime.php b/core/lib/Drupal/Core/Datetime/DrupalDateTime.php
index 2d4be46..7dd09d1 100644
--- a/core/lib/Drupal/Core/Datetime/DrupalDateTime.php
+++ b/core/lib/Drupal/Core/Datetime/DrupalDateTime.php
@@ -7,7 +7,6 @@
 namespace Drupal\Core\Datetime;
 
 use Drupal\Component\Datetime\DateTimePlus;
-use Drupal\Core\Language\Language;
 
 /**
  * Extends DateTimePlus().
@@ -53,7 +52,7 @@ class DrupalDateTime extends DateTimePlus {
   public function __construct($time = 'now', $timezone = NULL, $settings = array()) {
     // We can set the langcode and country using Drupal values.
     if (!isset($settings['langcode'])) {
-      $settings['langcode'] = \Drupal::languageManager()->getCurrentLanguage()->id;
+      $settings['langcode'] = \Drupal::languageManager()->getCurrentLanguage()->getId();
     }
 
     if (!isset($settings['country'])) {
diff --git a/core/lib/Drupal/Core/Entity/ContentEntityBase.php b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
index 1895cfd..2fed616 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\String;
 use Drupal\Core\Entity\Plugin\DataType\EntityReference;
 use Drupal\Core\Entity\TypedData\EntityDataDefinition;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
 
@@ -38,7 +38,7 @@
    * The plain data values of the contained fields.
    *
    * This always holds the original, unchanged values of the entity. The values
-   * are keyed by language code, whereas Language::LANGCODE_DEFAULT is used for
+   * are keyed by language code, whereas LanguageInterface::LANGCODE_DEFAULT is used for
    * values in default language.
    *
    * @todo: Add methods for getting original fields and for determining
@@ -80,7 +80,7 @@
    *
    * @var string
    */
-  protected $activeLangcode = Language::LANGCODE_DEFAULT;
+  protected $activeLangcode = LanguageInterface::LANGCODE_DEFAULT;
 
   /**
    * Local cache for the default language code.
@@ -141,22 +141,22 @@
   public function __construct(array $values, $entity_type, $bundle = FALSE, $translations = array()) {
     $this->entityTypeId = $entity_type;
     $this->entityKeys['bundle'] = $bundle ? $bundle : $this->entityTypeId;
-    $this->languages = $this->languageManager()->getLanguages(Language::STATE_ALL);
+    $this->languages = $this->languageManager()->getLanguages(LanguageInterface::STATE_ALL);
 
     foreach ($values as $key => $value) {
       // If the key matches an existing property set the value to the property
       // to set properties like isDefaultRevision.
       // @todo: Should this be converted somehow?
-      if (property_exists($this, $key) && isset($value[Language::LANGCODE_DEFAULT])) {
-        $this->$key = $value[Language::LANGCODE_DEFAULT];
+      if (property_exists($this, $key) && isset($value[LanguageInterface::LANGCODE_DEFAULT])) {
+        $this->$key = $value[LanguageInterface::LANGCODE_DEFAULT];
       }
     }
 
     $this->values = $values;
     foreach ($this->getEntityType()->getKeys() as $key => $field_name) {
       if (isset($this->values[$field_name])) {
-        if (is_array($this->values[$field_name]) && isset($this->values[$field_name][Language::LANGCODE_DEFAULT])) {
-          $this->entityKeys[$key] = $this->values[$field_name][Language::LANGCODE_DEFAULT];
+        if (is_array($this->values[$field_name]) && isset($this->values[$field_name][LanguageInterface::LANGCODE_DEFAULT])) {
+          $this->entityKeys[$key] = $this->values[$field_name][LanguageInterface::LANGCODE_DEFAULT];
         }
       }
     }
@@ -164,11 +164,11 @@ public function __construct(array $values, $entity_type, $bundle = FALSE, $trans
     // Initialize translations. Ensure we have at least an entry for the default
     // language.
     $data = array('status' => static::TRANSLATION_EXISTING);
-    $this->translations[Language::LANGCODE_DEFAULT] = $data;
+    $this->translations[LanguageInterface::LANGCODE_DEFAULT] = $data;
     $this->setDefaultLangcode();
     if ($translations) {
       foreach ($translations as $langcode) {
-        if ($langcode != $this->defaultLangcode && $langcode != Language::LANGCODE_DEFAULT) {
+        if ($langcode != $this->defaultLangcode && $langcode != LanguageInterface::LANGCODE_DEFAULT) {
           $this->translations[$langcode] = $data;
         }
       }
@@ -427,14 +427,14 @@ protected function getTranslatedField($name, $langcode) {
         throw new \InvalidArgumentException('Field ' . String::checkPlain($name) . ' is unknown.');
       }
       // Non-translatable fields are always stored with
-      // Language::LANGCODE_DEFAULT as key.
+      // LanguageInterface::LANGCODE_DEFAULT as key.
 
-      $default = $langcode == Language::LANGCODE_DEFAULT;
+      $default = $langcode == LanguageInterface::LANGCODE_DEFAULT;
       if (!$default && !$definition->isTranslatable()) {
-        if (!isset($this->fields[$name][Language::LANGCODE_DEFAULT])) {
-          $this->fields[$name][Language::LANGCODE_DEFAULT] = $this->getTranslatedField($name, Language::LANGCODE_DEFAULT);
+        if (!isset($this->fields[$name][LanguageInterface::LANGCODE_DEFAULT])) {
+          $this->fields[$name][LanguageInterface::LANGCODE_DEFAULT] = $this->getTranslatedField($name, LanguageInterface::LANGCODE_DEFAULT);
         }
-        $this->fields[$name][$langcode] = &$this->fields[$name][Language::LANGCODE_DEFAULT];
+        $this->fields[$name][$langcode] = &$this->fields[$name][LanguageInterface::LANGCODE_DEFAULT];
       }
       else {
         $value = NULL;
@@ -446,7 +446,7 @@ protected function getTranslatedField($name, $langcode) {
           // $this->defaultLangcode might not be set if we are initializing the
           // default language code cache, in which case there is no valid
           // langcode to assign.
-          $field_langcode = isset($this->defaultLangcode) ? $this->defaultLangcode : Language::LANGCODE_NOT_SPECIFIED;
+          $field_langcode = isset($this->defaultLangcode) ? $this->defaultLangcode : LanguageInterface::LANGCODE_NOT_SPECIFIED;
         }
         else {
           $field_langcode = $langcode;
@@ -554,9 +554,9 @@ public function access($operation, AccountInterface $account = NULL) {
    */
   public function language() {
     $language = NULL;
-    if ($this->activeLangcode != Language::LANGCODE_DEFAULT) {
+    if ($this->activeLangcode != LanguageInterface::LANGCODE_DEFAULT) {
       if (!isset($this->languages[$this->activeLangcode])) {
-        $this->languages += $this->languageManager()->getLanguages(Language::STATE_ALL);
+        $this->languages += $this->languageManager()->getLanguages(LanguageInterface::STATE_ALL);
       }
       $language = $this->languages[$this->activeLangcode];
     }
@@ -572,16 +572,16 @@ public function language() {
   protected function setDefaultLangcode() {
     // Get the language code if the property exists.
     if ($this->hasField('langcode') && ($item = $this->get('langcode')) && isset($item->language)) {
-      $this->defaultLangcode = $item->language->id;
+      $this->defaultLangcode = $item->language->getId();
     }
     if (empty($this->defaultLangcode)) {
       // Make sure we return a proper language object.
-      $this->defaultLangcode = Language::LANGCODE_NOT_SPECIFIED;
+      $this->defaultLangcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
     }
     // This needs to be initialized manually as it is skipped when instantiating
     // the language field object to avoid infinite recursion.
     if (!empty($this->fields['langcode'])) {
-      $this->fields['langcode'][Language::LANGCODE_DEFAULT]->setLangcode($this->defaultLangcode);
+      $this->fields['langcode'][LanguageInterface::LANGCODE_DEFAULT]->setLangcode($this->defaultLangcode);
     }
   }
 
@@ -593,8 +593,8 @@ protected function setDefaultLangcode() {
    */
   protected function updateFieldLangcodes($langcode) {
     foreach ($this->fields as $name => $items) {
-      if (!empty($items[Language::LANGCODE_DEFAULT])) {
-        $items[Language::LANGCODE_DEFAULT]->setLangcode($langcode);
+      if (!empty($items[LanguageInterface::LANGCODE_DEFAULT])) {
+        $items[LanguageInterface::LANGCODE_DEFAULT]->setLangcode($langcode);
       }
     }
   }
@@ -630,8 +630,8 @@ public function onChange($name) {
   public function getTranslation($langcode) {
     // Ensure we always use the default language code when dealing with the
     // original entity language.
-    if ($langcode != Language::LANGCODE_DEFAULT && $langcode == $this->defaultLangcode) {
-      $langcode = Language::LANGCODE_DEFAULT;
+    if ($langcode != LanguageInterface::LANGCODE_DEFAULT && $langcode == $this->defaultLangcode) {
+      $langcode = LanguageInterface::LANGCODE_DEFAULT;
     }
 
     // Populate entity translation object cache so it will be available for all
@@ -674,7 +674,7 @@ public function getTranslation($langcode) {
    * {@inheritdoc}
    */
   public function getUntranslated() {
-    return $this->getTranslation(Language::LANGCODE_DEFAULT);
+    return $this->getTranslation(LanguageInterface::LANGCODE_DEFAULT);
   }
 
   /**
@@ -721,7 +721,7 @@ protected function initializeTranslation($langcode) {
    */
   public function hasTranslation($langcode) {
     if ($langcode == $this->defaultLangcode) {
-      $langcode = Language::LANGCODE_DEFAULT;
+      $langcode = LanguageInterface::LANGCODE_DEFAULT;
     }
     return !empty($this->translations[$langcode]['status']);
   }
@@ -766,7 +766,7 @@ public function addTranslation($langcode, array $values = array()) {
    * {@inheritdoc}
    */
   public function removeTranslation($langcode) {
-    if (isset($this->translations[$langcode]) && $langcode != Language::LANGCODE_DEFAULT && $langcode != $this->defaultLangcode) {
+    if (isset($this->translations[$langcode]) && $langcode != LanguageInterface::LANGCODE_DEFAULT && $langcode != $this->defaultLangcode) {
       foreach ($this->getFieldDefinitions() as $name => $definition) {
         if ($definition->isTranslatable()) {
           unset($this->values[$name][$langcode]);
@@ -785,7 +785,7 @@ public function removeTranslation($langcode) {
    * {@inheritdoc}
    */
   public function initTranslation($langcode) {
-    if ($langcode != Language::LANGCODE_DEFAULT && $langcode != $this->defaultLangcode) {
+    if ($langcode != LanguageInterface::LANGCODE_DEFAULT && $langcode != $this->defaultLangcode) {
       $this->translations[$langcode]['status'] = static::TRANSLATION_EXISTING;
     }
   }
@@ -795,7 +795,7 @@ public function initTranslation($langcode) {
    */
   public function getTranslationLanguages($include_default = TRUE) {
     $translations = array_filter($this->translations, function($translation) { return $translation['status']; });
-    unset($translations[Language::LANGCODE_DEFAULT]);
+    unset($translations[LanguageInterface::LANGCODE_DEFAULT]);
 
     if ($include_default) {
       $translations[$this->defaultLangcode] = TRUE;
@@ -957,7 +957,7 @@ public function __clone() {
         // we retain just the original value, as references will be recreated
         // later as needed.
         if (!$definitions[$name]->isTranslatable() && count($values) > 1) {
-          $values = array_intersect_key($values, array(Language::LANGCODE_DEFAULT => TRUE));
+          $values = array_intersect_key($values, array(LanguageInterface::LANGCODE_DEFAULT => TRUE));
         }
         foreach ($values as $langcode => $items) {
           $this->fields[$name][$langcode] = clone $items;
diff --git a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
index da6890e..b4a8135 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Entity\Query\QueryInterface;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\field\FieldConfigUpdateForbiddenException;
 use Drupal\field\FieldConfigInterface;
 use Drupal\field\FieldInstanceConfigInterface;
@@ -163,12 +164,12 @@ protected function mapFromStorageRecords(array $records) {
         // that store several properties).
         if ($field_name = strstr($name, '__', TRUE)) {
           $property_name = substr($name, strpos($name, '__') + 2);
-          $entities[$id][$field_name][Language::LANGCODE_DEFAULT][$property_name] = $value;
+          $entities[$id][$field_name][LanguageInterface::LANGCODE_DEFAULT][$property_name] = $value;
         }
         else {
           // Handle columns named directly after the field (e.g if the field
           // type only stores one property).
-          $entities[$id][$name][Language::LANGCODE_DEFAULT] = $value;
+          $entities[$id][$name][LanguageInterface::LANGCODE_DEFAULT] = $value;
         }
       }
       // If we have no multilingual values we can instantiate entity objecs
@@ -209,7 +210,7 @@ protected function attachPropertyData(array &$entities) {
         // Get the revision IDs.
         $revision_ids = array();
         foreach ($entities as $values) {
-          $revision_ids[] = is_object($values) ? $values->getRevisionId() : $values[$this->revisionKey][Language::LANGCODE_DEFAULT];
+          $revision_ids[] = is_object($values) ? $values->getRevisionId() : $values[$this->revisionKey][LanguageInterface::LANGCODE_DEFAULT];
         }
         $query->condition($this->revisionKey, $revision_ids);
       }
@@ -228,8 +229,8 @@ protected function attachPropertyData(array &$entities) {
         $id = $values[$this->idKey];
 
         // Field values in default language are stored with
-        // Language::LANGCODE_DEFAULT as key.
-        $langcode = empty($values['default_langcode']) ? $values['langcode'] : Language::LANGCODE_DEFAULT;
+        // LanguageInterface::LANGCODE_DEFAULT as key.
+        $langcode = empty($values['default_langcode']) ? $values['langcode'] : LanguageInterface::LANGCODE_DEFAULT;
         $translations[$id][$langcode] = TRUE;
 
         foreach (array_keys($field_definitions) as $field_name) {
@@ -255,7 +256,7 @@ protected function attachPropertyData(array &$entities) {
       }
 
       foreach ($entities as $id => $values) {
-        $bundle = $this->bundleKey ? $values[$this->bundleKey][Language::LANGCODE_DEFAULT] : FALSE;
+        $bundle = $this->bundleKey ? $values[$this->bundleKey][LanguageInterface::LANGCODE_DEFAULT] : FALSE;
         // Turn the record into an entity class.
         $entities[$id] = new $this->entityClass($values, $this->entityTypeId, $bundle, array_keys($translations[$id]));
       }
@@ -650,9 +651,10 @@ protected function mapToStorageRecord(EntityInterface $entity, $table_key = 'bas
    *   The record to store.
    */
   protected function mapToDataStorageRecord(EntityInterface $entity, $table_key = 'data_table') {
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
     $record = $this->mapToStorageRecord($entity, $table_key);
-    $record->langcode = $entity->language()->id;
-    $record->default_langcode = intval($record->langcode == $entity->getUntranslated()->language()->id);
+    $record->langcode = $entity->language()->getId();
+    $record->default_langcode = intval($record->langcode == $entity->getUntranslated()->language()->getId());
     return $record;
   }
 
@@ -700,6 +702,7 @@ public function getQueryServiceName() {
    * {@inheritdoc}
    */
   protected function doLoadFieldItems($entities, $age) {
+    /** @var \Drupal\Core\Entity\ContentEntityInterface[] $entities */
     $load_current = $age == static::FIELD_LOAD_CURRENT;
 
     // Collect entities ids, bundles and languages.
@@ -709,7 +712,7 @@ protected function doLoadFieldItems($entities, $age) {
     foreach ($entities as $key => $entity) {
       $bundles[$entity->bundle()] = TRUE;
       $ids[] = $load_current ? $key : $entity->getRevisionId();
-      $default_langcodes[$key] = $entity->getUntranslated()->language()->id;
+      $default_langcodes[$key] = $entity->getUntranslated()->language()->getId();
     }
 
     // Collect impacted fields.
@@ -723,7 +726,7 @@ protected function doLoadFieldItems($entities, $age) {
     }
 
     // Load field data.
-    $langcodes = array_keys(language_list(Language::STATE_ALL));
+    $langcodes = array_keys(language_list(LanguageInterface::STATE_ALL));
     foreach ($fields as $field_name => $field) {
       $table = $load_current ? static::_fieldTableName($field) : static::_fieldRevisionTableName($field);
 
@@ -771,11 +774,12 @@ protected function doLoadFieldItems($entities, $age) {
    * {@inheritdoc}
    */
   protected function doSaveFieldItems(EntityInterface $entity, $update) {
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
     $vid = $entity->getRevisionId();
     $id = $entity->id();
     $bundle = $entity->bundle();
     $entity_type = $entity->getEntityTypeId();
-    $default_langcode = $entity->getUntranslated()->language()->id;
+    $default_langcode = $entity->getUntranslated()->language()->getId();
     $translation_langcodes = array_keys($entity->getTranslationLanguages());
 
     if (!isset($vid)) {
diff --git a/core/lib/Drupal/Core/Entity/ContentEntityForm.php b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
index 8722a9c..aa003d6 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityForm.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
@@ -90,7 +90,7 @@ public function getFormLangcode(array &$form_state) {
       // Imply a 'view' operation to ensure users edit entities in the same
       // language they are displayed. This allows to keep contextual editing
       // working also for multilingual entities.
-      $form_state['langcode'] = $this->entityManager->getTranslationFromContext($this->entity)->language()->id;
+      $form_state['langcode'] = $this->entityManager->getTranslationFromContext($this->entity)->language()->getId();
     }
     return $form_state['langcode'];
   }
@@ -99,7 +99,7 @@ public function getFormLangcode(array &$form_state) {
    * {@inheritdoc}
    */
   public function isDefaultFormLangcode(array $form_state) {
-    return $this->getFormLangcode($form_state) == $this->entity->getUntranslated()->language()->id;
+    return $this->getFormLangcode($form_state) == $this->entity->getUntranslated()->language()->getId();
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Entity/Entity.php b/core/lib/Drupal/Core/Entity/Entity.php
index a3f1ef7..fc99cce 100644
--- a/core/lib/Drupal/Core/Entity/Entity.php
+++ b/core/lib/Drupal/Core/Entity/Entity.php
@@ -15,6 +15,7 @@
 use Drupal\Core\Config\Entity\Exception\ConfigEntityIdLengthException;
 use Drupal\Core\Entity\Exception\UndefinedLinkTemplateException;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Url;
 
@@ -281,7 +282,7 @@ public function access($operation, AccountInterface $account = NULL) {
     }
     return $this->entityManager()
       ->getAccessController($this->entityTypeId)
-      ->access($this, $operation, Language::LANGCODE_DEFAULT, $account);
+      ->access($this, $operation, LanguageInterface::LANGCODE_DEFAULT, $account);
   }
 
   /**
@@ -291,7 +292,7 @@ public function language() {
     $language = $this->languageManager()->getLanguage($this->langcode);
     if (!$language) {
       // Make sure we return a proper language object.
-      $language = new Language(array('id' => Language::LANGCODE_NOT_SPECIFIED));
+      $language = new Language(array('id' => LanguageInterface::LANGCODE_NOT_SPECIFIED));
     }
     return $language;
   }
diff --git a/core/lib/Drupal/Core/Entity/EntityAccessController.php b/core/lib/Drupal/Core/Entity/EntityAccessController.php
index b092914..f20ef9c 100644
--- a/core/lib/Drupal/Core/Entity/EntityAccessController.php
+++ b/core/lib/Drupal/Core/Entity/EntityAccessController.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 
 /**
@@ -54,7 +54,7 @@ public function __construct(EntityTypeInterface $entity_type) {
   /**
    * {@inheritdoc}
    */
-  public function access(EntityInterface $entity, $operation, $langcode = Language::LANGCODE_DEFAULT, AccountInterface $account = NULL) {
+  public function access(EntityInterface $entity, $operation, $langcode = LanguageInterface::LANGCODE_DEFAULT, AccountInterface $account = NULL) {
     $account = $this->prepareUser($account);
 
     if (($access = $this->getCache($entity->uuid(), $operation, $langcode, $account)) !== NULL) {
@@ -203,7 +203,7 @@ public function resetCache() {
   public function createAccess($entity_bundle = NULL, AccountInterface $account = NULL, array $context = array()) {
     $account = $this->prepareUser($account);
     $context += array(
-      'langcode' => Language::LANGCODE_DEFAULT,
+      'langcode' => LanguageInterface::LANGCODE_DEFAULT,
     );
 
     $cid = $entity_bundle ? 'create:' . $entity_bundle : 'create';
diff --git a/core/lib/Drupal/Core/Entity/EntityAccessControllerInterface.php b/core/lib/Drupal/Core/Entity/EntityAccessControllerInterface.php
index 6bc8a23..62bba90 100644
--- a/core/lib/Drupal/Core/Entity/EntityAccessControllerInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityAccessControllerInterface.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 
 /**
@@ -31,7 +31,7 @@
    *   Usually one of "view", "update" or "delete".
    * @param string $langcode
    *   (optional) The language code for which to check access. Defaults to
-   *   Language::LANGCODE_DEFAULT.
+   *   LanguageInterface::LANGCODE_DEFAULT.
    * @param \Drupal\Core\Session\AccountInterface $account
    *   (optional) The user session for which to check access, or NULL to check
    *   access for the current user. Defaults to NULL.
@@ -39,7 +39,7 @@
    * @return bool
    *   TRUE if access was granted, FALSE otherwise.
    */
-  public function access(EntityInterface $entity, $operation, $langcode = Language::LANGCODE_DEFAULT, AccountInterface $account = NULL);
+  public function access(EntityInterface $entity, $operation, $langcode = LanguageInterface::LANGCODE_DEFAULT, AccountInterface $account = NULL);
 
   /**
    * Checks access to create an entity.
diff --git a/core/lib/Drupal/Core/Entity/EntityForm.php b/core/lib/Drupal/Core/Entity/EntityForm.php
index dcb9aae..7982e8b 100644
--- a/core/lib/Drupal/Core/Entity/EntityForm.php
+++ b/core/lib/Drupal/Core/Entity/EntityForm.php
@@ -145,7 +145,7 @@ public function form(array $form, array &$form_state) {
       // new entities.
       $form['langcode'] = array(
         '#type' => 'value',
-        '#value' => !$entity->isNew() ? $entity->language()->id : language_default()->id,
+        '#value' => !$entity->isNew() ? $entity->language()->getId() : language_default()->getId(),
       );
     }
     return $form;
@@ -287,7 +287,7 @@ public function save(array $form, array &$form_state) {
    * {@inheritdoc}
    */
   public function getFormLangcode(array &$form_state) {
-    return $this->entity->language()->id;
+    return $this->entity->language()->getId();
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Entity/EntityInterface.php b/core/lib/Drupal/Core/Entity/EntityInterface.php
index ab62144..e235488 100644
--- a/core/lib/Drupal/Core/Entity/EntityInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityInterface.php
@@ -37,7 +37,7 @@ public function id();
   /**
    * Returns the language of the entity.
    *
-   * @return \Drupal\Core\Language\Language
+   * @return \Drupal\Core\Language\LanguageInterface
    *   The language object.
    */
   public function language();
diff --git a/core/lib/Drupal/Core/Entity/EntityManager.php b/core/lib/Drupal/Core/Entity/EntityManager.php
index 3fe2c54..0624e60 100644
--- a/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -17,7 +17,7 @@
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Language\LanguageManager;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Plugin\Discovery\AlterDecorator;
 use Drupal\Core\Plugin\Discovery\CacheDecorator;
 use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
@@ -173,7 +173,7 @@ public function __construct(\Traversable $namespaces, ModuleHandlerInterface $mo
     $this->discovery = new AnnotatedClassDiscovery('Entity', $namespaces, 'Drupal\Core\Entity\Annotation\EntityType');
     $this->discovery = new InfoHookDecorator($this->discovery, 'entity_type_build');
     $this->discovery = new AlterDecorator($this->discovery, 'entity_type');
-    $this->discovery = new CacheDecorator($this->discovery, 'entity_type:' . $this->languageManager->getCurrentLanguage()->id, 'discovery', Cache::PERMANENT, array('entity_types' => TRUE));
+    $this->discovery = new CacheDecorator($this->discovery, 'entity_type:' . $this->languageManager->getCurrentLanguage()->getId(), 'discovery', Cache::PERMANENT, array('entity_types' => TRUE));
 
   }
 
@@ -329,7 +329,7 @@ public function getBaseFieldDefinitions($entity_type_id) {
     // Check the static cache.
     if (!isset($this->baseFieldDefinitions[$entity_type_id])) {
       // Not prepared, try to load from cache.
-      $cid = 'entity_base_field_definitions:' . $entity_type_id . ':' . $this->languageManager->getCurrentLanguage()->id;
+      $cid = 'entity_base_field_definitions:' . $entity_type_id . ':' . $this->languageManager->getCurrentLanguage()->getId();
       if ($cache = $this->cache->get($cid)) {
         $this->baseFieldDefinitions[$entity_type_id] = $cache->data;
       }
@@ -425,7 +425,7 @@ public function getFieldDefinitions($entity_type_id, $bundle) {
     if (!isset($this->fieldDefinitions[$entity_type_id][$bundle])) {
       $base_field_definitions = $this->getBaseFieldDefinitions($entity_type_id);
       // Not prepared, try to load from cache.
-      $cid = 'entity_bundle_field_definitions:' . $entity_type_id . ':' . $bundle . ':' . $this->languageManager->getCurrentLanguage()->id;
+      $cid = 'entity_bundle_field_definitions:' . $entity_type_id . ':' . $bundle . ':' . $this->languageManager->getCurrentLanguage()->getId();
       if ($cache = $this->cache->get($cid)) {
         $bundle_field_definitions = $cache->data;
       }
@@ -517,7 +517,7 @@ public function getFieldStorageDefinitions($entity_type_id) {
         }
       }
       // Not prepared, try to load from cache.
-      $cid = 'entity_field_storage_definitions:' . $entity_type_id . ':' . $this->languageManager->getCurrentLanguage()->id;
+      $cid = 'entity_field_storage_definitions:' . $entity_type_id . ':' . $this->languageManager->getCurrentLanguage()->getId();
       if ($cache = $this->cache->get($cid)) {
         $field_storage_definitions = $cache->data;
       }
@@ -621,7 +621,7 @@ public function getBundleInfo($entity_type) {
    */
   public function getAllBundleInfo() {
     if (!isset($this->bundleInfo)) {
-      $langcode = $this->languageManager->getCurrentLanguage()->id;
+      $langcode = $this->languageManager->getCurrentLanguage()->getId();
       if ($cache = $this->cache->get("entity_bundle_info:$langcode")) {
         $this->bundleInfo = $cache->data;
       }
@@ -662,7 +662,7 @@ public function getExtraFields($entity_type_id, $bundle) {
     // Read from the persistent cache. Since hook_entity_extra_field_info() and
     // hook_entity_extra_field_info_alter() might contain t() calls, we cache
     // per language.
-    $cache_id = 'entity_bundle_extra_fields:' . $entity_type_id . ':' . $bundle . ':' . $this->languageManager->getCurrentLanguage()->id;
+    $cache_id = 'entity_bundle_extra_fields:' . $entity_type_id . ':' . $bundle . ':' . $this->languageManager->getCurrentLanguage()->getId();
     $cached = $this->cache->get($cache_id);
     if ($cached) {
       $this->extraFields[$entity_type_id][$bundle] = $cached->data;
@@ -724,7 +724,7 @@ public function getTranslationFromContext(EntityInterface $entity, $langcode = N
 
     if ($entity instanceof TranslatableInterface) {
       if (empty($langcode)) {
-        $langcode = $this->languageManager->getCurrentLanguage(Language::TYPE_CONTENT)->id;
+        $langcode = $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();
       }
 
       // Retrieve language fallback candidates to perform the entity language
@@ -735,7 +735,7 @@ public function getTranslationFromContext(EntityInterface $entity, $langcode = N
 
       // Ensure the default language has the proper language code.
       $default_language = $entity->getUntranslated()->language();
-      $candidates[$default_language->id] = Language::LANGCODE_DEFAULT;
+      $candidates[$default_language->getId()] = LanguageInterface::LANGCODE_DEFAULT;
 
       // Return the most fitting entity translation.
       foreach ($candidates as $candidate) {
@@ -789,7 +789,7 @@ public function getFormModes($entity_type_id) {
   protected function getAllDisplayModesByEntityType($display_type) {
     if (!isset($this->displayModeInfo[$display_type])) {
       $key = 'entity_' . $display_type . '_info';
-      $langcode = $this->languageManager->getCurrentLanguage(Language::TYPE_INTERFACE)->id;
+      $langcode = $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_INTERFACE)->getId();
       if ($cache = $this->cache->get("$key:$langcode")) {
         $this->displayModeInfo[$display_type] = $cache->data;
       }
diff --git a/core/lib/Drupal/Core/Entity/EntityViewBuilder.php b/core/lib/Drupal/Core/Entity/EntityViewBuilder.php
index cd1cbfb..b5b05f9 100644
--- a/core/lib/Drupal/Core/Entity/EntityViewBuilder.php
+++ b/core/lib/Drupal/Core/Entity/EntityViewBuilder.php
@@ -13,7 +13,7 @@
 use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Field\FieldItemInterface;
 use Drupal\Core\Field\FieldItemListInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\Core\TypedData\TranslatableInterface;
 use Drupal\Core\Render\Element;
@@ -109,7 +109,7 @@ public function view(EntityInterface $entity, $view_mode = 'full', $langcode = N
    */
   public function viewMultiple(array $entities = array(), $view_mode = 'full', $langcode = NULL) {
     if (!isset($langcode)) {
-      $langcode = $this->languageManager->getCurrentLanguage(Language::TYPE_CONTENT)->id;
+      $langcode = $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();
     }
 
     $build_list = array(
diff --git a/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php b/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php
index 442162c..30c65ca 100644
--- a/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php
+++ b/core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php
@@ -94,7 +94,7 @@ public static function createInstance(ContainerInterface $container, EntityTypeI
    */
   public function doCreate(array $values = array()) {
     // Set default language to site default if not provided.
-    $values += array('langcode' => $this->languageManager->getDefaultLanguage()->id);
+    $values += array('langcode' => $this->languageManager->getDefaultLanguage()->getId());
     $entity = new $this->entityClass($values, $this->entityTypeId);
 
     // @todo This is handled by ContentEntityStorageBase, which assumes
diff --git a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
index 3063bb2..37322ec 100644
--- a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
@@ -9,7 +9,6 @@
 
 use Drupal\Core\Config\Config;
 use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\Core\Site\Settings;
 use Symfony\Component\HttpFoundation\Request;
@@ -70,7 +69,7 @@ public function onRespond(FilterResponseEvent $event) {
     $response->headers->set('X-UA-Compatible', 'IE=edge,chrome=1', FALSE);
 
     // Set the Content-language header.
-    $response->headers->set('Content-language', $this->languageManager->getCurrentLanguage()->id);
+    $response->headers->set('Content-language', $this->languageManager->getCurrentLanguage()->getId());
 
     // Attach globally-declared headers to the response object so that Symfony
     // can send them for us correctly.
diff --git a/core/lib/Drupal/Core/Field/FieldItemList.php b/core/lib/Drupal/Core/Field/FieldItemList.php
index 39be1ee..2e0b442 100644
--- a/core/lib/Drupal/Core/Field/FieldItemList.php
+++ b/core/lib/Drupal/Core/Field/FieldItemList.php
@@ -11,7 +11,7 @@
 use Drupal\Core\TypedData\DataDefinitionInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\Core\TypedData\Plugin\DataType\ItemList;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Represents an entity field; that is, a list of field item objects.
@@ -36,7 +36,7 @@ class FieldItemList extends ItemList implements FieldItemListInterface {
    *
    * @var string
    */
-  protected $langcode = Language::LANGCODE_NOT_SPECIFIED;
+  protected $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
 
   /**
    * {@inheritdoc}
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php
index e3192b2..719a0d6 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Field\FieldItemBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\TypedData\DataDefinition;
 use Drupal\Core\TypedData\DataReferenceDefinition;
 
@@ -92,7 +92,7 @@ public function setValue($values, $notify = TRUE) {
    */
   public function applyDefaultValue($notify = TRUE) {
     // Default to LANGCODE_NOT_SPECIFIED.
-    $this->setValue(array('value' => Language::LANGCODE_NOT_SPECIFIED), $notify);
+    $this->setValue(array('value' => LanguageInterface::LANGCODE_NOT_SPECIFIED), $notify);
     return $this;
   }
 
diff --git a/core/lib/Drupal/Core/Language/Language.php b/core/lib/Drupal/Core/Language/Language.php
index 4575983..c291a4e 100644
--- a/core/lib/Drupal/Core/Language/Language.php
+++ b/core/lib/Drupal/Core/Language/Language.php
@@ -35,14 +35,14 @@ class Language implements LanguageInterface {
    *
    * @var string
    */
-  public $name = '';
+  protected $name = '';
 
   /**
    * The ID, langcode.
    *
    * @var string
    */
-  public $id = '';
+  protected $id = '';
 
   /**
    * The direction, left-to-right, or right-to-left.
@@ -51,21 +51,21 @@ class Language implements LanguageInterface {
    *
    * @var int
    */
-  public $direction = self::DIRECTION_LTR;
+  protected $direction = self::DIRECTION_LTR;
 
   /**
    * The weight, used for ordering languages in lists, like selects or tables.
    *
    * @var int
    */
-  public $weight = 0;
+  protected $weight = 0;
 
   /**
    * Flag indicating if this is the only site default language.
    *
    * @var bool
    */
-  public $default = FALSE;
+  protected $default = FALSE;
 
   /**
    * The language negotiation method used when a language was detected.
@@ -75,7 +75,7 @@ class Language implements LanguageInterface {
    *
    * @var string
    */
-  public $method_id;
+  protected $negotiationMethodId;
 
   /**
    * Locked indicates a language used by the system, not an actual language.
@@ -86,7 +86,7 @@ class Language implements LanguageInterface {
    *
    * @var bool
    */
-  public $locked = FALSE;
+  protected $locked = FALSE;
 
   /**
    * Constructs a new class instance.
@@ -197,26 +197,43 @@ public function setDefault($default) {
    * {@inheritdoc}
    */
   public function getNegotiationMethodId() {
-    return $this->method_id;
+    return $this->negotiationMethodId;
   }
 
   /**
    * {@inheritdoc}
    */
   public function setNegotiationMethodId($method_id) {
-    $this->method_id = $method_id;
+    $this->negotiationMethodId = $method_id;
 
     return $this;
   }
 
   /**
+   * {@inheritdoc}
+   */
+  public function isLocked() {
+    return $this->locked;
+  }
+
+  /**
    * Sort language objects.
    *
-   * @param array $languages
-   *   The array of language objects keyed by langcode.
+   * This is a sort() callback.
+   *
+   * @param \Drupal\Core\Language\LanguageInterface $a
+   * @param \Drupal\Core\Language\LanguageInterface $b
+   *
+   * @return int
+   *   -1, 0, or 1.
    */
-  public static function sort(&$languages) {
-    uasort($languages, 'Drupal\Component\Utility\SortArray::sortByWeightAndTitleKey');
+  public static function sort(LanguageInterface $a, LanguageInterface $b) {
+    if ($a->getWeight() == $b->getWeight()) {
+      return strnatcasecmp($a->getName(), $b->getName());
+    }
+    else {
+      return $a->getWeight() < $b->getWeight() ? -1 : 1;
+    }
   }
 
 }
diff --git a/core/lib/Drupal/Core/Language/LanguageDefault.php b/core/lib/Drupal/Core/Language/LanguageDefault.php
index a72b8b1..53f40d2 100644
--- a/core/lib/Drupal/Core/Language/LanguageDefault.php
+++ b/core/lib/Drupal/Core/Language/LanguageDefault.php
@@ -22,7 +22,7 @@ class LanguageDefault {
   /**
    * The default language.
    *
-   * @var \Drupal\Core\Language\Language
+   * @var \Drupal\Core\Language\LanguageInterface
    */
   protected $language;
 
@@ -39,7 +39,7 @@ public function __construct(array $values) {
   /**
    * Gets the default language.
    *
-   * @return \Drupal\Core\Language\Language
+   * @return \Drupal\Core\Language\LanguageInterface
    *   The default language.
    */
   public function get() {
@@ -49,11 +49,11 @@ public function get() {
   /**
    * Sets the default language.
    *
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   The default language.
    */
-  public function set(Language $language) {
-    $language->default = TRUE;
+  public function set(LanguageInterface $language) {
+    $language->setDefault(TRUE);
     $this->language = $language;
   }
 
diff --git a/core/lib/Drupal/Core/Language/LanguageInterface.php b/core/lib/Drupal/Core/Language/LanguageInterface.php
index e718749..d3977b4 100644
--- a/core/lib/Drupal/Core/Language/LanguageInterface.php
+++ b/core/lib/Drupal/Core/Language/LanguageInterface.php
@@ -208,4 +208,17 @@ public function getNegotiationMethodId();
    */
   public function setNegotiationMethodId($method_id);
 
+  /**
+   * Checks if the language is locked.
+   *
+   * Locked indicates a language used by the system, not an actual language.
+   * Examples of locked languages are, LANGCODE_NOT_SPECIFIED, und, and
+   * LANGCODE_NOT_APPLICABLE, zxx, which are usually shown in language selects
+   * but hidden in places like the Language configuration and cannot be deleted.
+   *
+   * @return bool
+   *   TRUE if the language is locked.
+   */
+  public function isLocked();
+
 }
diff --git a/core/lib/Drupal/Core/Language/LanguageManager.php b/core/lib/Drupal/Core/Language/LanguageManager.php
index 3d943d0..d738f5a 100644
--- a/core/lib/Drupal/Core/Language/LanguageManager.php
+++ b/core/lib/Drupal/Core/Language/LanguageManager.php
@@ -26,7 +26,7 @@ class LanguageManager extends DependencySerialization implements LanguageManager
   /**
    * An array of all the available languages keyed by language code.
    *
-   * @var array
+   * @var \Drupal\Core\Language\LanguageInterface[]
    */
   protected $languages;
 
@@ -40,7 +40,7 @@ class LanguageManager extends DependencySerialization implements LanguageManager
   /**
    * Constructs the language manager.
    *
-   * @param \Drupal\Core\Language\Language $default_language
+   * @param \Drupal\Core\Language\LanguageDefault $default_language
    *   The default language.
    */
   public function __construct(LanguageDefault $default_language) {
@@ -80,13 +80,13 @@ public function isMultilingual() {
    * {@inheritdoc}
    */
   public function getLanguageTypes() {
-    return array(Language::TYPE_INTERFACE, Language::TYPE_CONTENT, Language::TYPE_URL);
+    return array(LanguageInterface::TYPE_INTERFACE, LanguageInterface::TYPE_CONTENT, LanguageInterface::TYPE_URL);
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getCurrentLanguage($type = Language::TYPE_INTERFACE) {
+  public function getCurrentLanguage($type = LanguageInterface::TYPE_INTERFACE) {
     return $this->getDefaultLanguage();
   }
 
@@ -107,14 +107,14 @@ public function getDefaultLanguage() {
   /**
    * {@inheritdoc}
    */
-  public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
+  public function getLanguages($flags = LanguageInterface::STATE_CONFIGURABLE) {
     // Initialize master language list.
     if (!isset($this->languages)) {
       // No language module, so use the default language only.
       $default = $this->getDefaultLanguage();
-      $this->languages = array($default->id => $default);
+      $this->languages = array($default->getId() => $default);
       // Add the special languages, they will be filtered later if needed.
-      $this->languages += $this->getDefaultLockedLanguages($default->weight);
+      $this->languages += $this->getDefaultLockedLanguages($default->getWeight());
     }
 
     // Filter the full list of languages based on the value of the $all flag. By
@@ -123,15 +123,15 @@ public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
     $filtered_languages = array();
 
     // Add the site's default language if flagged as allowed value.
-    if ($flags & Language::STATE_SITE_DEFAULT) {
+    if ($flags & LanguageInterface::STATE_SITE_DEFAULT) {
       $default = isset($default) ? $default : $this->getDefaultLanguage();
       // Rename the default language.
-      $default->name = $this->t("Site's default language (@lang_name)", array('@lang_name' => $default->name));
+      $default->setName($this->t("Site's default language (@lang_name)", array('@lang_name' => $default->getName())));
       $filtered_languages['site_default'] = $default;
     }
 
     foreach ($this->languages as $id => $language) {
-      if (($language->locked && ($flags & Language::STATE_LOCKED)) || (!$language->locked && ($flags & Language::STATE_CONFIGURABLE))) {
+      if (($language->isLocked() && ($flags & LanguageInterface::STATE_LOCKED)) || (!$language->isLocked() && ($flags & LanguageInterface::STATE_CONFIGURABLE))) {
         $filtered_languages[$id] = $language;
       }
     }
@@ -143,7 +143,7 @@ public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
    * {@inheritdoc}
    */
   public function getLanguage($langcode) {
-    $languages = $this->getLanguages(Language::STATE_ALL);
+    $languages = $this->getLanguages(LanguageInterface::STATE_ALL);
     return isset($languages[$langcode]) ? $languages[$langcode] : NULL;
   }
 
@@ -151,11 +151,11 @@ public function getLanguage($langcode) {
    * {@inheritdoc}
    */
   public function getLanguageName($langcode) {
-    if ($langcode == Language::LANGCODE_NOT_SPECIFIED) {
+    if ($langcode == LanguageInterface::LANGCODE_NOT_SPECIFIED) {
       return $this->t('None');
     }
     if ($language = $this->getLanguage($langcode)) {
-      return $language->name;
+      return $language->getName();
     }
     if (empty($langcode)) {
       return $this->t('Unknown');
@@ -173,14 +173,14 @@ public function getDefaultLockedLanguages($weight = 0) {
       'default' => FALSE,
       'locked' => TRUE,
     );
-    $languages[Language::LANGCODE_NOT_SPECIFIED] = new Language(array(
-      'id' => Language::LANGCODE_NOT_SPECIFIED,
+    $languages[LanguageInterface::LANGCODE_NOT_SPECIFIED] = new Language(array(
+      'id' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'name' => $this->t('Not specified'),
       'weight' => ++$weight,
     ) + $locked_language);
 
-    $languages[Language::LANGCODE_NOT_APPLICABLE] = new Language(array(
-      'id' => Language::LANGCODE_NOT_APPLICABLE,
+    $languages[LanguageInterface::LANGCODE_NOT_APPLICABLE] = new Language(array(
+      'id' => LanguageInterface::LANGCODE_NOT_APPLICABLE,
       'name' => $this->t('Not applicable'),
       'weight' => ++$weight,
     ) + $locked_language);
@@ -193,14 +193,14 @@ public function getDefaultLockedLanguages($weight = 0) {
    */
   public function isLanguageLocked($langcode) {
     $language = $this->getLanguage($langcode);
-    return ($language ? $language->locked : FALSE);
+    return ($language ? $language->isLocked() : FALSE);
   }
 
   /**
    * {@inheritdoc}
    */
   public function getFallbackCandidates($langcode = NULL, array $context = array()) {
-    return array(Language::LANGCODE_DEFAULT);
+    return array(LanguageInterface::LANGCODE_DEFAULT);
   }
 
   /**
@@ -235,7 +235,7 @@ public static function getStandardLanguageList() {
     return array(
       'af' => array('Afrikaans', 'Afrikaans'),
       'am' => array('Amharic', 'አማርኛ'),
-      'ar' => array('Arabic', /* Left-to-right marker "‭" */ 'العربية', Language::DIRECTION_RTL),
+      'ar' => array('Arabic', /* Left-to-right marker "‭" */ 'العربية', LanguageInterface::DIRECTION_RTL),
       'ast' => array('Asturian', 'Asturianu'),
       'az' => array('Azerbaijani', 'Azərbaycanca'),
       'be' => array('Belarusian', 'Беларуская'),
@@ -255,7 +255,7 @@ public static function getStandardLanguageList() {
       'es' => array('Spanish', 'Español'),
       'et' => array('Estonian', 'Eesti'),
       'eu' => array('Basque', 'Euskera'),
-      'fa' => array('Persian, Farsi', /* Left-to-right marker "‭" */ 'فارسی', Language::DIRECTION_RTL),
+      'fa' => array('Persian, Farsi', /* Left-to-right marker "‭" */ 'فارسی', LanguageInterface::DIRECTION_RTL),
       'fi' => array('Finnish', 'Suomi'),
       'fil' => array('Filipino', 'Filipino'),
       'fo' => array('Faeroese', 'Føroyskt'),
@@ -266,7 +266,7 @@ public static function getStandardLanguageList() {
       'gl' => array('Galician', 'Galego'),
       'gsw-berne' => array('Swiss German', 'Schwyzerdütsch'),
       'gu' => array('Gujarati', 'ગુજરાતી'),
-      'he' => array('Hebrew', /* Left-to-right marker "‭" */ 'עברית', Language::DIRECTION_RTL),
+      'he' => array('Hebrew', /* Left-to-right marker "‭" */ 'עברית', LanguageInterface::DIRECTION_RTL),
       'hi' => array('Hindi', 'हिन्दी'),
       'hr' => array('Croatian', 'Hrvatski'),
       'ht' => array('Haitian Creole', 'Kreyòl ayisyen'),
@@ -322,7 +322,7 @@ public static function getStandardLanguageList() {
       'tyv' => array('Tuvan', 'Тыва дыл'),
       'ug' => array('Uyghur', 'Уйғур'),
       'uk' => array('Ukrainian', 'Українська'),
-      'ur' => array('Urdu', /* Left-to-right marker "‭" */ 'اردو', Language::DIRECTION_RTL),
+      'ur' => array('Urdu', /* Left-to-right marker "‭" */ 'اردو', LanguageInterface::DIRECTION_RTL),
       'vi' => array('Vietnamese', 'Tiếng Việt'),
       'xx-lolspeak' => array('Lolspeak', 'Lolspeak'),
       'zh-hans' => array('Chinese, Simplified', '简体中文'),
@@ -339,7 +339,7 @@ public static function getStandardLanguageList() {
    *
    * @see \Drupal\language\ConfigurableLanguageManager::setConfigOverrideLanguage()
    */
-  public function setConfigOverrideLanguage(Language $language = NULL) {
+  public function setConfigOverrideLanguage(LanguageInterface $language = NULL) {
     return $this;
   }
 
diff --git a/core/lib/Drupal/Core/Language/LanguageManagerInterface.php b/core/lib/Drupal/Core/Language/LanguageManagerInterface.php
index 43b2f23..a37327d 100644
--- a/core/lib/Drupal/Core/Language/LanguageManagerInterface.php
+++ b/core/lib/Drupal/Core/Language/LanguageManagerInterface.php
@@ -48,19 +48,19 @@ public function getLanguageTypes();
    *
    * @param string $type
    *   (optional) The language type, e.g. the interface or the content language.
-   *   Defaults to \Drupal\Core\Language\Language::TYPE_INTERFACE.
+   *   Defaults to \Drupal\Core\Language\LanguageInterface::TYPE_INTERFACE.
    *
-   * @return \Drupal\Core\Language\Language
+   * @return \Drupal\Core\Language\LanguageInterface
    *   A language object for the given type.
    */
-  public function getCurrentLanguage($type = Language::TYPE_INTERFACE);
+  public function getCurrentLanguage($type = LanguageInterface::TYPE_INTERFACE);
 
   /**
    * Resets the given language type or all types if none specified.
    *
    * @param string|null $type
    *   (optional) The language type to reset as a string, e.g.,
-   *   Language::TYPE_INTERFACE, or NULL to reset all language types. Defaults
+   *   LanguageInterface::TYPE_INTERFACE, or NULL to reset all language types. Defaults
    *   to NULL.
    *
    * @return \Drupal\Core\Language\LanguageManagerInterface
@@ -71,7 +71,7 @@ public function reset($type = NULL);
   /**
    * Returns a language object representing the site's default language.
    *
-   * @return \Drupal\Core\Language\Language
+   * @return \Drupal\Core\Language\LanguageInterface
    *   A language object.
    */
   public function getDefaultLanguage();
@@ -81,13 +81,13 @@ public function getDefaultLanguage();
    *
    * @param int $flags
    *   (optional) Specifies the state of the languages that have to be returned.
-   *   It can be: Language::STATE_CONFIGURABLE,
-   *   Language::STATE_LOCKED, Language::STATE_ALL.
+   *   It can be: LanguageInterface::STATE_CONFIGURABLE,
+   *   LanguageInterface::STATE_LOCKED, LanguageInterface::STATE_ALL.
    *
-   * @return array
+   * @return \Drupal\Core\Language\LanguageInterface[]
    *   An associative array of languages, keyed by the language code.
    */
-  public function getLanguages($flags = Language::STATE_CONFIGURABLE);
+  public function getLanguages($flags = LanguageInterface::STATE_CONFIGURABLE);
 
   /**
    * Returns a language object from the given language code.
@@ -95,7 +95,7 @@ public function getLanguages($flags = Language::STATE_CONFIGURABLE);
    * @param string $langcode
    *   The language code.
    *
-   * @return \Drupal\core\Language\Language|null
+   * @return \Drupal\core\Language\LanguageInterface|null
    *   A fully-populated language object or NULL.
    */
   public function getLanguage($langcode);
@@ -170,17 +170,17 @@ public function getLanguageSwitchLinks($type, $path);
   /**
    * Sets the configuration override language.
    *
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   The language to override configuration with.
    *
    * @return $this
    */
-  public function setConfigOverrideLanguage(Language $language = NULL);
+  public function setConfigOverrideLanguage(LanguageInterface $language = NULL);
 
   /**
    * Gets the current configuration override language.
    *
-   * @return \Drupal\Core\Language\Language $language
+   * @return \Drupal\Core\Language\LanguageInterface
    *   The current configuration override language.
    */
   public function getConfigOverrideLanguage();
diff --git a/core/lib/Drupal/Core/Page/DefaultHtmlFragmentRenderer.php b/core/lib/Drupal/Core/Page/DefaultHtmlFragmentRenderer.php
index 74ed87b..b4b8300 100644
--- a/core/lib/Drupal/Core/Page/DefaultHtmlFragmentRenderer.php
+++ b/core/lib/Drupal/Core/Page/DefaultHtmlFragmentRenderer.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\Core\Page;
 
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManager;
 
 /**
@@ -82,8 +81,8 @@ public function preparePage(HtmlPage $page, &$page_array) {
     // HTML element attributes.
     $language_interface = $this->languageManager->getCurrentLanguage();
     $html_attributes = $page->getHtmlAttributes();
-    $html_attributes['lang'] = $language_interface->id;
-    $html_attributes['dir'] = $language_interface->direction ? 'rtl' : 'ltr';
+    $html_attributes['lang'] = $language_interface->getId();
+    $html_attributes['dir'] = $language_interface->getDirection() ? 'rtl' : 'ltr';
 
     $this->setDefaultMetaTags($page);
 
diff --git a/core/lib/Drupal/Core/Path/AliasManager.php b/core/lib/Drupal/Core/Path/AliasManager.php
index 55d2ddc..8d1a8e6 100644
--- a/core/lib/Drupal/Core/Path/AliasManager.php
+++ b/core/lib/Drupal/Core/Path/AliasManager.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\Core\Path;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManager;
 
 class AliasManager implements AliasManagerInterface {
@@ -95,7 +95,7 @@ public function getPathByAlias($alias, $langcode = NULL) {
     // language. If we used a language different from the one conveyed by the
     // requested URL, we might end up being unable to check if there is a path
     // alias matching the URL path.
-    $langcode = $langcode ?: $this->languageManager->getCurrentLanguage(Language::TYPE_URL)->id;
+    $langcode = $langcode ?: $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_URL)->getId();
 
     // If we already know that there are no paths for this alias simply return.
     if (empty($alias) || !empty($this->noPath[$langcode][$alias])) {
@@ -127,7 +127,7 @@ public function getAliasByPath($path, $langcode = NULL) {
     // language. If we used a language different from the one conveyed by the
     // requested URL, we might end up being unable to check if there is a path
     // alias matching the URL path.
-    $langcode = $langcode ?: $this->languageManager->getCurrentLanguage(Language::TYPE_URL)->id;
+    $langcode = $langcode ?: $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_URL)->getId();
 
     // Check the path whitelist, if the top-level part before the first /
     // is not in the list, then there is no need to do anything further,
diff --git a/core/lib/Drupal/Core/Path/AliasStorage.php b/core/lib/Drupal/Core/Path/AliasStorage.php
index aa6989c..b405a25 100644
--- a/core/lib/Drupal/Core/Path/AliasStorage.php
+++ b/core/lib/Drupal/Core/Path/AliasStorage.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Database\Connection;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Provides a class for CRUD operations on path aliases.
@@ -46,7 +46,7 @@ public function __construct(Connection $connection, ModuleHandlerInterface $modu
   /**
    * {@inheritdoc}
    */
-  public function save($source, $alias, $langcode = Language::LANGCODE_NOT_SPECIFIED, $pid = NULL) {
+  public function save($source, $alias, $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED, $pid = NULL) {
 
     $fields = array(
       'source' => $source,
@@ -114,7 +114,7 @@ public function preloadPathAlias($preloaded, $langcode) {
     $args = array(
       ':system' => $preloaded,
       ':langcode' => $langcode,
-      ':langcode_undetermined' => Language::LANGCODE_NOT_SPECIFIED,
+      ':langcode_undetermined' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     );
     // Always get the language-specific alias before the language-neutral one.
     // For example 'de' is less than 'und' so the order needs to be ASC, while
@@ -123,12 +123,12 @@ public function preloadPathAlias($preloaded, $langcode) {
     // created alias for each source. Subsequent queries using fetchField() must
     // use pid DESC to have the same effect. For performance reasons, the query
     // builder is not used here.
-    if ($langcode == Language::LANGCODE_NOT_SPECIFIED) {
+    if ($langcode == LanguageInterface::LANGCODE_NOT_SPECIFIED) {
       // Prevent PDO from complaining about a token the query doesn't use.
       unset($args[':langcode']);
       $result = $this->connection->query('SELECT source, alias FROM {url_alias} WHERE source IN (:system) AND langcode = :langcode_undetermined ORDER BY pid ASC', $args);
     }
-    elseif ($langcode < Language::LANGCODE_NOT_SPECIFIED) {
+    elseif ($langcode < LanguageInterface::LANGCODE_NOT_SPECIFIED) {
       $result = $this->connection->query('SELECT source, alias FROM {url_alias} WHERE source IN (:system) AND langcode IN (:langcode, :langcode_undetermined) ORDER BY langcode ASC, pid ASC', $args);
     }
     else {
@@ -145,14 +145,14 @@ public function lookupPathAlias($path, $langcode) {
     $args = array(
       ':source' => $path,
       ':langcode' => $langcode,
-      ':langcode_undetermined' => Language::LANGCODE_NOT_SPECIFIED,
+      ':langcode_undetermined' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     );
     // See the queries above.
-    if ($langcode == Language::LANGCODE_NOT_SPECIFIED) {
+    if ($langcode == LanguageInterface::LANGCODE_NOT_SPECIFIED) {
       unset($args[':langcode']);
       $alias = $this->connection->query("SELECT alias FROM {url_alias} WHERE source = :source AND langcode = :langcode_undetermined ORDER BY pid DESC", $args)->fetchField();
     }
-    elseif ($langcode > Language::LANGCODE_NOT_SPECIFIED) {
+    elseif ($langcode > LanguageInterface::LANGCODE_NOT_SPECIFIED) {
       $alias = $this->connection->query("SELECT alias FROM {url_alias} WHERE source = :source AND langcode IN (:langcode, :langcode_undetermined) ORDER BY langcode DESC, pid DESC", $args)->fetchField();
     }
     else {
@@ -169,14 +169,14 @@ public function lookupPathSource($path, $langcode) {
     $args = array(
       ':alias' => $path,
       ':langcode' => $langcode,
-      ':langcode_undetermined' => Language::LANGCODE_NOT_SPECIFIED,
+      ':langcode_undetermined' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     );
     // See the queries above.
-    if ($langcode == Language::LANGCODE_NOT_SPECIFIED) {
+    if ($langcode == LanguageInterface::LANGCODE_NOT_SPECIFIED) {
       unset($args[':langcode']);
       $result = $this->connection->query("SELECT source FROM {url_alias} WHERE alias = :alias AND langcode = :langcode_undetermined ORDER BY pid DESC", $args);
     }
-    elseif ($langcode > Language::LANGCODE_NOT_SPECIFIED) {
+    elseif ($langcode > LanguageInterface::LANGCODE_NOT_SPECIFIED) {
       $result = $this->connection->query("SELECT source FROM {url_alias} WHERE alias = :alias AND langcode IN (:langcode, :langcode_undetermined) ORDER BY langcode DESC, pid DESC", $args);
     }
     else {
@@ -217,7 +217,7 @@ public function aliasExists($alias, $langcode, $source = NULL) {
    *   TRUE if aliases with language exist.
    */
   public function languageAliasExists() {
-    return (bool) $this->connection->queryRange('SELECT 1 FROM {url_alias} WHERE langcode <> :langcode', 0, 1, array(':langcode' => Language::LANGCODE_NOT_SPECIFIED))->fetchField();
+    return (bool) $this->connection->queryRange('SELECT 1 FROM {url_alias} WHERE langcode <> :langcode', 0, 1, array(':langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED))->fetchField();
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Path/AliasStorageInterface.php b/core/lib/Drupal/Core/Path/AliasStorageInterface.php
index 68c7cdd..a98600f 100644
--- a/core/lib/Drupal/Core/Path/AliasStorageInterface.php
+++ b/core/lib/Drupal/Core/Path/AliasStorageInterface.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\Core\Path;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Provides a class for CRUD operations on path aliases.
@@ -34,7 +34,7 @@
    *   - pid (int): Unique path alias identifier.
    *   - langcode (string): The language code of the alias.
    */
-  public function save($source, $alias, $langcode = Language::LANGCODE_NOT_SPECIFIED, $pid = NULL);
+  public function save($source, $alias, $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED, $pid = NULL);
 
   /**
    * Fetches a specific URL alias from the database.
diff --git a/core/lib/Drupal/Core/PathProcessor/PathProcessorAlias.php b/core/lib/Drupal/Core/PathProcessor/PathProcessorAlias.php
index 1c709a1..67226ab 100644
--- a/core/lib/Drupal/Core/PathProcessor/PathProcessorAlias.php
+++ b/core/lib/Drupal/Core/PathProcessor/PathProcessorAlias.php
@@ -45,7 +45,7 @@ public function processInbound($path, Request $request) {
    */
   public function processOutbound($path, &$options = array(), Request $request = NULL) {
     if (empty($options['alias'])) {
-      $langcode = isset($options['language']) ? $options['language']->id : NULL;
+      $langcode = isset($options['language']) ? $options['language']->getId() : NULL;
       $path = $this->aliasManager->getAliasByPath($path, $langcode);
     }
     return $path;
diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index e9c4ce9..ff6bfff 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -16,7 +16,6 @@
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
 use Drupal\Core\Plugin\Factory\ContainerFactory;
 
@@ -146,7 +145,7 @@ public function setCacheBackend(CacheBackendInterface $cache_backend, LanguageMa
     $this->languageManager = $language_manager;
     $this->cacheBackend = $cache_backend;
     $this->cacheKeyPrefix = $cache_key_prefix;
-    $this->cacheKey = $cache_key_prefix . ':' . $language_manager->getCurrentLanguage()->id;
+    $this->cacheKey = $cache_key_prefix . ':' . $language_manager->getCurrentLanguage()->getId();
     $this->cacheTags = $cache_tags;
   }
 
diff --git a/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php b/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php
index 686f0d3..b191729 100644
--- a/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php
+++ b/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php
@@ -55,7 +55,7 @@
    *   - 'language': An optional language object. If the path being linked to is
    *     internal to the site, $options['language'] is used to look up the alias
    *     for the URL. If $options['language'] is omitted, the language will be
-   *     obtained from \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_URL).
+   *     obtained from \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_URL).
    *   - 'https': Whether this URL should point to a secure location. If not
    *     defined, the current scheme is used, so the user stays on HTTP or HTTPS
    *     respectively. TRUE enforces HTTPS and FALSE enforces HTTP, but HTTPS can
@@ -122,7 +122,7 @@ public function getPathFromRoute($name, $parameters = array());
    *     displayed outside the site, such as in an RSS feed.
    *   - 'language': An optional language object used to look up the alias
    *     for the URL. If $options['language'] is omitted, it defaults to the
-   *     current language for the language type Language::TYPE_URL.
+   *     current language for the language type LanguageInterface::TYPE_URL.
    *   - 'https': Whether this URL should point to a secure location. If not
    *     defined, the current scheme is used, so the user stays on HTTP or HTTPS
    *     respectively. if mixed mode sessions are permitted, TRUE enforces HTTPS
diff --git a/core/lib/Drupal/Core/Session/UserSession.php b/core/lib/Drupal/Core/Session/UserSession.php
index 704fc79..a1a8cd0 100644
--- a/core/lib/Drupal/Core/Session/UserSession.php
+++ b/core/lib/Drupal/Core/Session/UserSession.php
@@ -193,10 +193,10 @@ public function isAnonymous() {
   function getPreferredLangcode($default = NULL) {
     $language_list = language_list();
     if (!empty($this->preferred_langcode) && isset($language_list[$this->preferred_langcode])) {
-      return $language_list[$this->preferred_langcode]->id;
+      return $language_list[$this->preferred_langcode]->getId();
     }
     else {
-      return $default ? $default : language_default()->id;
+      return $default ? $default : language_default()->getId();
     }
   }
 
@@ -206,10 +206,10 @@ function getPreferredLangcode($default = NULL) {
   function getPreferredAdminLangcode($default = NULL) {
     $language_list = language_list();
     if (!empty($this->preferred_admin_langcode) && isset($language_list[$this->preferred_admin_langcode])) {
-      return $language_list[$this->preferred_admin_langcode]->id;
+      return $language_list[$this->preferred_admin_langcode]->getId();
     }
     else {
-      return $default ? $default : language_default()->id;
+      return $default ? $default : language_default()->getId();
     }
   }
 
diff --git a/core/lib/Drupal/Core/StringTranslation/TranslationManager.php b/core/lib/Drupal/Core/StringTranslation/TranslationManager.php
index bd1b3b3..f8b6bb1 100644
--- a/core/lib/Drupal/Core/StringTranslation/TranslationManager.php
+++ b/core/lib/Drupal/Core/StringTranslation/TranslationManager.php
@@ -60,7 +60,7 @@ class TranslationManager implements TranslationInterface, TranslatorInterface {
    */
   public function __construct(LanguageManagerInterface $language_manager) {
     $this->languageManager = $language_manager;
-    $this->defaultLangcode = $language_manager->getDefaultLanguage()->id;
+    $this->defaultLangcode = $language_manager->getDefaultLanguage()->getId();
   }
 
   /**
diff --git a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php
index 510a869..8be31e5 100644
--- a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php
+++ b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Language.php
@@ -57,7 +57,7 @@ public function getValue() {
   public function setValue($value, $notify = TRUE) {
     // Support passing language objects.
     if (is_object($value)) {
-      $this->id = $value->id;
+      $this->id = $value->getId();
       $this->language = $value;
     }
     elseif (isset($value) && !is_scalar($value)) {
diff --git a/core/lib/Drupal/Core/TypedData/TranslatableInterface.php b/core/lib/Drupal/Core/TypedData/TranslatableInterface.php
index 8632edb..557a17e 100644
--- a/core/lib/Drupal/Core/TypedData/TranslatableInterface.php
+++ b/core/lib/Drupal/Core/TypedData/TranslatableInterface.php
@@ -29,7 +29,7 @@ public function language();
    *   (optional) Whether the default language should be included. Defaults to
    *   TRUE.
    *
-   * @return
+   * @return \Drupal\Core\Language\LanguageInterface[]
    *   An array of language objects, keyed by language codes.
    */
   public function getTranslationLanguages($include_default = TRUE);
@@ -42,7 +42,7 @@ public function getTranslationLanguages($include_default = TRUE);
    * instantiated.
    *
    * @param $langcode
-   *   The language code of the translation to get or Language::LANGCODE_DEFAULT
+   *   The language code of the translation to get or LanguageInterface::LANGCODE_DEFAULT
    *   to get the data in default language.
    *
    * @return \Drupal\Core\TypedData\TypedDataInterface
diff --git a/core/lib/Drupal/Core/Url.php b/core/lib/Drupal/Core/Url.php
index 93b329a..f7f2b1a 100644
--- a/core/lib/Drupal/Core/Url.php
+++ b/core/lib/Drupal/Core/Url.php
@@ -83,7 +83,7 @@ class Url extends DependencySerialization {
    *     displayed outside the site, such as in an RSS feed.
    *   - 'language': An optional language object used to look up the alias
    *     for the URL. If $options['language'] is omitted, it defaults to the
-   *     current language for the language type Language::TYPE_URL.
+   *     current language for the language type LanguageInterface::TYPE_URL.
    *   - 'https': Whether this URL should point to a secure location. If not
    *     defined, the current scheme is used, so the user stays on HTTP or HTTPS
    *     respectively. if mixed mode sessions are permitted, TRUE enforces HTTPS
diff --git a/core/lib/Drupal/Core/Utility/LinkGenerator.php b/core/lib/Drupal/Core/Utility/LinkGenerator.php
index b547d95..2c38b45 100644
--- a/core/lib/Drupal/Core/Utility/LinkGenerator.php
+++ b/core/lib/Drupal/Core/Utility/LinkGenerator.php
@@ -81,7 +81,7 @@ public function generateFromUrl($text, Url $url) {
     // Add a hreflang attribute if we know the language of this link's url and
     // hreflang has not already been set.
     if (!empty($variables['options']['language']) && !isset($variables['options']['attributes']['hreflang'])) {
-      $variables['options']['attributes']['hreflang'] = $variables['options']['language']->id;
+      $variables['options']['attributes']['hreflang'] = $variables['options']['language']->getId();
     }
 
     // Set the "active" class if the 'set_active_class' option is not empty.
diff --git a/core/lib/Drupal/Core/Utility/Token.php b/core/lib/Drupal/Core/Utility/Token.php
index 4a1238e..73376e1 100644
--- a/core/lib/Drupal/Core/Utility/Token.php
+++ b/core/lib/Drupal/Core/Utility/Token.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
 
 /**
@@ -311,7 +311,7 @@ public function findWithPrefix(array $tokens, $prefix, $delimiter = ':') {
    */
   public function getInfo() {
     if (is_null($this->tokenInfo)) {
-      $cache_id = 'token_info:' . $this->languageManager->getCurrentLanguage(Language::TYPE_CONTENT)->id;
+      $cache_id = 'token_info:' . $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();
       $cache = $this->cache->get($cache_id);
       if ($cache) {
         $this->tokenInfo = $cache->data;
diff --git a/core/lib/Drupal/Core/Validation/DrupalTranslator.php b/core/lib/Drupal/Core/Validation/DrupalTranslator.php
index 5b4d99d..84847a5 100644
--- a/core/lib/Drupal/Core/Validation/DrupalTranslator.php
+++ b/core/lib/Drupal/Core/Validation/DrupalTranslator.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\Core\Validation;
 
-use Drupal\Core\Language\Language;
 use Symfony\Component\Translation\TranslatorInterface;
 
 /**
@@ -56,7 +55,7 @@ public function setLocale($locale) {
    * Implements \Symfony\Component\Translation\TranslatorInterface::getLocale().
    */
   public function getLocale() {
-    return $this->locale ? $this->locale : \Drupal::languageManager()->getCurrentLanguage()->id;
+    return $this->locale ? $this->locale : \Drupal::languageManager()->getCurrentLanguage()->getId();
   }
 
   /**
diff --git a/core/modules/aggregator/aggregator.install b/core/modules/aggregator/aggregator.install
index e4bef0e..028f8cd 100644
--- a/core/modules/aggregator/aggregator.install
+++ b/core/modules/aggregator/aggregator.install
@@ -4,7 +4,6 @@
  * @file
  * Install, update and uninstall functions for the aggregator module.
  */
-use Drupal\Core\Language\Language;
 
 /**
  * Implements hook_requirements().
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedForm.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedForm.php
index 1770f03..f2f35aa 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/FeedForm.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedForm.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\String;
 use Drupal\Core\Entity\ContentEntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
@@ -30,8 +30,8 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#title' => $this->t('Language'),
       '#type' => 'language_select',
-      '#default_value' => $feed->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#default_value' => $feed->language()->getId(),
+      '#languages' => LanguageInterface::STATE_ALL,
       '#weight' => -4,
     );
 
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/aggregator/processor/DefaultProcessor.php b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/aggregator/processor/DefaultProcessor.php
index 058ba18..13de3e0 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/aggregator/processor/DefaultProcessor.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/aggregator/processor/DefaultProcessor.php
@@ -190,7 +190,7 @@ public function process(FeedInterface $feed) {
         $entry = reset($entry);
       }
       else {
-        $entry = entity_create('aggregator_item', array('langcode' => $feed->language()->id));
+        $entry = entity_create('aggregator_item', array('langcode' => $feed->language()->getId()));
       }
       if ($item['timestamp']) {
         $entry->setPostedTime($item['timestamp']);
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorTestBase.php b/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorTestBase.php
index 6a85657..fe052e4 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorTestBase.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Tests/AggregatorTestBase.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\aggregator\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 use Drupal\aggregator\FeedInterface;
 
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Tests/FeedLanguageTest.php b/core/modules/aggregator/lib/Drupal/aggregator/Tests/FeedLanguageTest.php
index d297abc..29a1863 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Tests/FeedLanguageTest.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Tests/FeedLanguageTest.php
@@ -24,7 +24,7 @@ class FeedLanguageTest extends AggregatorTestBase {
   /**
    * List of langcodes.
    *
-   * @var array
+   * @var \Drupal\Core\Language\LanguageInterface[]
    */
   protected $langcodes = array();
 
@@ -55,14 +55,15 @@ public function setUp() {
    * Tests creation of feeds with a language.
    */
   public function testFeedLanguage() {
+    /** @var \Drupal\aggregator\FeedInterface[] $feeds */
     $feeds = array();
     // Create feeds.
-    $feeds[1] = $this->createFeed(NULL, array('langcode' => $this->langcodes[1]->id));
-    $feeds[2] = $this->createFeed(NULL, array('langcode' => $this->langcodes[2]->id));
+    $feeds[1] = $this->createFeed(NULL, array('langcode' => $this->langcodes[1]->getId()));
+    $feeds[2] = $this->createFeed(NULL, array('langcode' => $this->langcodes[2]->getId()));
 
     // Make sure that the language has been assigned.
-    $this->assertEqual($feeds[1]->language()->id, $this->langcodes[1]->id);
-    $this->assertEqual($feeds[2]->language()->id, $this->langcodes[2]->id);
+    $this->assertEqual($feeds[1]->language()->getId(), $this->langcodes[1]->getId());
+    $this->assertEqual($feeds[2]->language()->getId(), $this->langcodes[2]->getId());
 
     // Create example nodes to create feed items from and then update the feeds.
     $this->createSampleNodes();
@@ -71,10 +72,11 @@ public function testFeedLanguage() {
     // Loop over the created feed items and verify that their language matches
     // the one from the feed.
     foreach ($feeds as $feed) {
+      /** @var \Drupal\aggregator\ItemInterface[] $items */
       $items = entity_load_multiple_by_properties('aggregator_item', array('fid' => $feed->id()));
       $this->assertTrue(count($items) > 0, 'Feed items were created.');
       foreach ($items as $item) {
-        $this->assertEqual($item->language()->id, $feed->language()->id);
+        $this->assertEqual($item->language()->getId(), $feed->language()->getId());
       }
     }
   }
diff --git a/core/modules/block/block.install b/core/modules/block/block.install
index a53a120..0d1ca69 100644
--- a/core/modules/block/block.install
+++ b/core/modules/block/block.install
@@ -5,8 +5,6 @@
  * Install, update and uninstall functions for the block module.
  */
 
-use Drupal\Core\Language\Language;
-
 /**
  * Implements hook_install().
  */
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockForm.php b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockForm.php
index f495c4f..090f529 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockForm.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockForm.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Entity\ContentEntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManager;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -102,15 +102,15 @@ public function form(array $form, array &$form_state) {
       // Set the correct default language.
       if ($block->isNew()) {
         $language_default = $this->languageManager->getCurrentLanguage($language_configuration['langcode']);
-        $block->langcode->value = $language_default->id;
+        $block->langcode->value = $language_default->getId();
       }
     }
 
     $form['langcode'] = array(
       '#title' => $this->t('Language'),
       '#type' => 'language_select',
-      '#default_value' => $block->getUntranslated()->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#default_value' => $block->getUntranslated()->language()->getId(),
+      '#languages' => LanguageInterface::STATE_ALL,
       '#access' => isset($language_configuration['language_show']) && $language_configuration['language_show'],
     );
 
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockSaveTest.php b/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockSaveTest.php
index ff0192e..aa18c5d 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockSaveTest.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockSaveTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\custom_block\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests block save related functionality.
  */
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockTypeTest.php b/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockTypeTest.php
index 896ad7c..5bdbf92 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockTypeTest.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockTypeTest.php
@@ -66,7 +66,7 @@ public function testCustomBlockTypeCreation() {
     $this->assertTrue($block_type, 'The new block type has been created.');
 
     // Check that the block type was created in site default language.
-    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
+    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
     $this->assertEqual($block_type->langcode, $default_langcode);
   }
 
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/PageEditTest.php b/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/PageEditTest.php
index 8062fb5..e39c81f 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/PageEditTest.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/PageEditTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\custom_block\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests the block edit functionality.
  */
diff --git a/core/modules/block/lib/Drupal/block/BlockAccessController.php b/core/modules/block/lib/Drupal/block/BlockAccessController.php
index 9e4e472..6f2c951 100644
--- a/core/modules/block/lib/Drupal/block/BlockAccessController.php
+++ b/core/modules/block/lib/Drupal/block/BlockAccessController.php
@@ -117,7 +117,7 @@ protected function checkAccess(EntityInterface $entity, $operation, $langcode, A
 
     // Language visibility settings.
     if (!empty($visibility['language']['langcodes']) && array_filter($visibility['language']['langcodes'])) {
-      if (empty($visibility['language']['langcodes'][\Drupal::languageManager()->getCurrentLanguage($visibility['language']['language_type'])->id])) {
+      if (empty($visibility['language']['langcodes'][\Drupal::languageManager()->getCurrentLanguage($visibility['language']['language_type'])->getId()])) {
         return FALSE;
       }
     }
diff --git a/core/modules/block/lib/Drupal/block/BlockBase.php b/core/modules/block/lib/Drupal/block/BlockBase.php
index e50a18c..6989a4a 100644
--- a/core/modules/block/lib/Drupal/block/BlockBase.php
+++ b/core/modules/block/lib/Drupal/block/BlockBase.php
@@ -11,7 +11,7 @@
 use Drupal\block\BlockInterface;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Component\Utility\NestedArray;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheableInterface;
 use Drupal\Core\Session\AccountInterface;
@@ -262,7 +262,7 @@ public function getMachineNameSuggestion() {
     //   \Drupal\system\MachineNameController::transliterate(), so it might make
     //   sense to provide a common service for the two.
     $transliteration_service = \Drupal::transliteration();
-    $transliterated = $transliteration_service->transliterate($admin_label, Language::LANGCODE_DEFAULT, '_');
+    $transliterated = $transliteration_service->transliterate($admin_label, LanguageInterface::LANGCODE_DEFAULT, '_');
 
     $replace_pattern = '[^a-z0-9_.]+';
 
diff --git a/core/modules/block/lib/Drupal/block/BlockForm.php b/core/modules/block/lib/Drupal/block/BlockForm.php
index d614dce..aded250 100644
--- a/core/modules/block/lib/Drupal/block/BlockForm.php
+++ b/core/modules/block/lib/Drupal/block/BlockForm.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -157,12 +157,12 @@ public function form(array $form, array &$form_state) {
       $language_types = $this->languageManager->getLanguageTypes();
 
       // Fetch languages.
-      $languages = $this->languageManager->getLanguages(Language::STATE_ALL);
+      $languages = $this->languageManager->getLanguages(LanguageInterface::STATE_ALL);
       $langcodes_options = array();
       foreach ($languages as $language) {
-        // @todo $language->name is not wrapped with t(), it should be replaced
+        // @todo $language->getName() is not wrapped with t(), it should be replaced
         //   by CMI translation implementation.
-        $langcodes_options[$language->id] = $language->name;
+        $langcodes_options[$language->getId()] = $language->getName();
       }
       $form['visibility']['language'] = array(
         '#type' => 'details',
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
index 65d67f6..48f5a18 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
@@ -93,7 +93,7 @@ protected function createTests() {
       'id' => 'test_block',
       'weight' => NULL,
       'status' => TRUE,
-      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->id,
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
       'dependencies' => array('module' => array('block_test'), 'theme' => array('stark')),
       'theme' => 'stark',
       'region' => '-1',
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index 9cc4835..fcd8459 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -11,7 +11,7 @@
 use Drupal\Core\Render\Element;
 use Drupal\node\NodeInterface;
 use Drupal\node\NodeTypeInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
 use Drupal\Core\Template\Attribute;
 use Symfony\Component\HttpFoundation\Request;
@@ -491,13 +491,13 @@ function template_preprocess_book_export_html(&$variables) {
   $variables['title'] = String::checkPlain($variables['title']);
   $variables['base_url'] = $base_url;
   $variables['language'] = $language_interface;
-  $variables['language_rtl'] = ($language_interface->direction == Language::DIRECTION_RTL);
+  $variables['language_rtl'] = ($language_interface->getDirection() == LanguageInterface::DIRECTION_RTL);
   $variables['head'] = drupal_get_html_head();
 
   // HTML element attributes.
   $attributes = array();
-  $attributes['lang'] = $language_interface->id;
-  $attributes['dir'] = $language_interface->direction ? 'rtl' : 'ltr';
+  $attributes['lang'] = $language_interface->getId();
+  $attributes['dir'] = $language_interface->getDirection() ? 'rtl' : 'ltr';
   $variables['html_attributes'] = new Attribute($attributes);
 }
 
diff --git a/core/modules/book/lib/Drupal/book/BookManager.php b/core/modules/book/lib/Drupal/book/BookManager.php
index c491cf4..84a43d2 100644
--- a/core/modules/book/lib/Drupal/book/BookManager.php
+++ b/core/modules/book/lib/Drupal/book/BookManager.php
@@ -465,7 +465,7 @@ public function bookTreeAllData($bid, $link = NULL, $max_depth = NULL) {
     $nid = isset($link['nid']) ? $link['nid'] : 0;
     // Generate a cache ID (cid) specific for this $bid, $link, $language, and
     // depth.
-    $cid = 'book-links:' . $bid . ':all:' . $nid . ':' . $language_interface->id . ':' . (int) $max_depth;
+    $cid = 'book-links:' . $bid . ':all:' . $nid . ':' . $language_interface->getId() . ':' . (int) $max_depth;
 
     if (!isset($tree[$cid])) {
       // If the tree data was not in the static cache, build $tree_parameters.
@@ -618,7 +618,7 @@ protected function doBookTreeBuild($bid, array $parameters = array()) {
     if (isset($parameters['expanded'])) {
       sort($parameters['expanded']);
     }
-    $tree_cid = 'book-links:' . $bid . ':tree-data:' . $language_interface->id . ':' . hash('sha256', serialize($parameters));
+    $tree_cid = 'book-links:' . $bid . ':tree-data:' . $language_interface->getId() . ':' . hash('sha256', serialize($parameters));
 
     // If we do not have this tree in the static cache, check {cache_data}.
     if (!isset($trees[$tree_cid])) {
diff --git a/core/modules/ckeditor/ckeditor.admin.inc b/core/modules/ckeditor/ckeditor.admin.inc
index 373ebd2..a4b779d 100644
--- a/core/modules/ckeditor/ckeditor.admin.inc
+++ b/core/modules/ckeditor/ckeditor.admin.inc
@@ -5,7 +5,6 @@
  * Callbacks and theming for the CKEditor toolbar configuration UI.
  */
 
-use Drupal\Core\Language\Language;
 use Drupal\Core\Template\Attribute;
 
 /**
@@ -21,7 +20,7 @@
 function template_preprocess_ckeditor_settings_toolbar(&$variables) {
   // Simplify the language direction information for toolbar buttons.
   $language_interface = \Drupal::languageManager()->getCurrentLanguage();
-  $language_direction = $language_interface->direction ? 'rtl' : 'ltr';
+  $language_direction = $language_interface->getDirection() ? 'rtl' : 'ltr';
 
   // Create lists of active and disabled buttons.
   $editor = $variables['editor'];
diff --git a/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
index cc6af2f..8f5642a 100644
--- a/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
@@ -10,7 +10,6 @@
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\ckeditor\CKEditorPluginManager;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\Core\Render\Element;
 use Drupal\editor\Plugin\EditorBase;
@@ -271,8 +270,8 @@ public function getJSSettings(EditorEntity $editor) {
     // Map the interface language code to a CKEditor translation.
     $ckeditor_langcodes = $this->getLangcodes();
     $language_interface = $this->languageManager->getCurrentLanguage();
-    if (isset($ckeditor_langcodes[$language_interface->id])) {
-      $display_langcode = $ckeditor_langcodes[$language_interface->id];
+    if (isset($ckeditor_langcodes[$language_interface->getId()])) {
+      $display_langcode = $ckeditor_langcodes[$language_interface->getId()];
     }
 
     // Next, set the most fundamental CKEditor settings.
diff --git a/core/modules/comment/lib/Drupal/comment/CommentForm.php b/core/modules/comment/lib/Drupal/comment/CommentForm.php
index 6fd7ff6..9199a8e 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentForm.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentForm.php
@@ -14,7 +14,7 @@
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Entity\ContentEntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -64,8 +64,8 @@ protected function init(array &$form_state) {
     // Make the comment inherit the current content language unless specifically
     // set.
     if ($comment->isNew()) {
-      $language_content = \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT);
-      $comment->langcode->value = $language_content->id;
+      $language_content = \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
+      $comment->langcode->value = $language_content->getId();
     }
 
     parent::init($form_state);
diff --git a/core/modules/comment/lib/Drupal/comment/CommentViewBuilder.php b/core/modules/comment/lib/Drupal/comment/CommentViewBuilder.php
index 5a75d43..b79a088 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentViewBuilder.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentViewBuilder.php
@@ -15,7 +15,6 @@
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Entity\EntityViewBuilder;
 use Drupal\entity\Entity\EntityViewDisplay;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
diff --git a/core/modules/comment/lib/Drupal/comment/Entity/Comment.php b/core/modules/comment/lib/Drupal/comment/Entity/Comment.php
index de10346..3eb2a7b 100644
--- a/core/modules/comment/lib/Drupal/comment/Entity/Comment.php
+++ b/core/modules/comment/lib/Drupal/comment/Entity/Comment.php
@@ -13,7 +13,6 @@
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Field\FieldDefinition;
-use Drupal\Core\Language\Language;
 use Drupal\Core\TypedData\DataDefinition;
 use Drupal\user\UserInterface;
 
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentCSSTest.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentCSSTest.php
index 8c2df9b..8c34754 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentCSSTest.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentCSSTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\comment\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\comment\CommentInterface;
 
 /**
@@ -59,8 +59,8 @@ function testCommentClasses() {
         'uid' => $case['comment_uid'],
         'status' => $case['comment_status'],
         'subject' => $this->randomName(),
-        'language' => Language::LANGCODE_NOT_SPECIFIED,
-        'comment_body' => array(Language::LANGCODE_NOT_SPECIFIED => array($this->randomName())),
+        'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+        'comment_body' => array(LanguageInterface::LANGCODE_NOT_SPECIFIED => array($this->randomName())),
       ));
       $comment->save();
 
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentLinksTest.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentLinksTest.php
index cf7af82..bce2746 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentLinksTest.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentLinksTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\comment\Tests;
 
 use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\comment\CommentInterface;
 
 /**
@@ -152,8 +152,8 @@ function setEnvironment(array $info) {
           'status' => CommentInterface::PUBLISHED,
           'subject' => $this->randomName(),
           'hostname' => '127.0.0.1',
-          'langcode' => Language::LANGCODE_NOT_SPECIFIED,
-          'comment_body' => array(Language::LANGCODE_NOT_SPECIFIED => array($this->randomName())),
+          'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+          'comment_body' => array(LanguageInterface::LANGCODE_NOT_SPECIFIED => array($this->randomName())),
         ));
         $comment->save();
         $this->comment = $comment;
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentNewIndicatorTest.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentNewIndicatorTest.php
index fbe36d2..f955b62 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentNewIndicatorTest.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentNewIndicatorTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\comment\Tests;
 
 use Drupal\Component\Serialization\Json;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\comment\CommentInterface;
 
 /**
@@ -100,8 +100,8 @@ public function testCommentNewCommentsIndicator() {
       'status' => CommentInterface::PUBLISHED,
       'subject' => $this->randomName(),
       'hostname' => '127.0.0.1',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
-      'comment_body' => array(Language::LANGCODE_NOT_SPECIFIED => array($this->randomName())),
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
+      'comment_body' => array(LanguageInterface::LANGCODE_NOT_SPECIFIED => array($this->randomName())),
     ));
     $comment->save();
     $this->drupalLogout();
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentTestBase.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentTestBase.php
index c1edf13..29f2033 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentTestBase.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentTestBase.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\comment\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\comment\CommentInterface;
 use Drupal\simpletest\WebTestBase;
 
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentThreadingTest.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentThreadingTest.php
index f69b55f..85c2342 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentThreadingTest.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentThreadingTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\comment\Tests;
 
-use Drupal\Core\Language\Language;
 
 /**
  * Tests comment threading.
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentTokenReplaceTest.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentTokenReplaceTest.php
index 0d2a4b2..d126998 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentTokenReplaceTest.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentTokenReplaceTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\comment\Tests;
 
 use Drupal\Component\Utility\Xss;
-use Drupal\Core\Language\Language;
 
 /**
  * Tests comment token replacement in strings.
@@ -63,8 +62,8 @@ function testCommentTokenReplacement() {
     $tests['[comment:body]'] = $comment->comment_body->processed;
     $tests['[comment:url]'] = url('comment/' . $comment->id(), $url_options + array('fragment' => 'comment-' . $comment->id()));
     $tests['[comment:edit-url]'] = url('comment/' . $comment->id() . '/edit', $url_options);
-    $tests['[comment:created:since]'] = format_interval(REQUEST_TIME - $comment->getCreatedTime(), 2, $language_interface->id);
-    $tests['[comment:changed:since]'] = format_interval(REQUEST_TIME - $comment->getChangedTime(), 2, $language_interface->id);
+    $tests['[comment:created:since]'] = format_interval(REQUEST_TIME - $comment->getCreatedTime(), 2, $language_interface->getId());
+    $tests['[comment:changed:since]'] = format_interval(REQUEST_TIME - $comment->getChangedTime(), 2, $language_interface->getId());
     $tests['[comment:parent:cid]'] = $comment->hasParentComment() ? $comment->getParentComment()->id() : NULL;
     $tests['[comment:parent:title]'] = check_plain($parent_comment->getSubject());
     $tests['[comment:node:nid]'] = $comment->getCommentedEntityId();
@@ -76,7 +75,7 @@ function testCommentTokenReplacement() {
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('comment' => $comment), array('langcode' => $language_interface->id));
+      $output = $token_service->replace($input, array('comment' => $comment), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Sanitized comment token %token replaced.', array('%token' => $input)));
     }
 
@@ -93,7 +92,7 @@ function testCommentTokenReplacement() {
     $tests['[comment:author:name]'] = $this->admin_user->getUsername();
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('comment' => $comment), array('langcode' => $language_interface->id, 'sanitize' => FALSE));
+      $output = $token_service->replace($input, array('comment' => $comment), array('langcode' => $language_interface->getId(), 'sanitize' => FALSE));
       $this->assertEqual($output, $expected, format_string('Unsanitized comment token %token replaced.', array('%token' => $input)));
     }
 
@@ -108,7 +107,7 @@ function testCommentTokenReplacement() {
     $tests['[node:comment-count]'] = 2;
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('entity' => $node, 'node' => $node), array('langcode' => $language_interface->id));
+      $output = $token_service->replace($input, array('entity' => $node, 'node' => $node), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Node comment token %token replaced.', array('%token' => $input)));
     }
   }
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
index f3ca94f..ba1bffe 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
@@ -12,7 +12,6 @@
 use Drupal\Core\Entity\EntityStorageException;
 use Drupal\Core\Config\Entity\ConfigEntityStorage;
 use Drupal\Core\Config\Entity\Exception\ConfigEntityIdLengthException;
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -44,7 +43,7 @@ public static function getInfo() {
    * Tests CRUD operations.
    */
   function testCRUD() {
-    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
+    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
     // Verify default properties on a newly created empty entity.
     $empty = entity_create('config_test');
     $this->assertIdentical($empty->id, NULL);
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php
index b95a666..88c4a13 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php
@@ -63,7 +63,7 @@ function testImport() {
       'test_dependencies' => array(),
       'status' => TRUE,
       'uuid' => '30df59bd-7b03-4cf7-bb35-d42fc49f0651',
-      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->id,
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
       'dependencies' => array(),
       'protected_property' => '',
     );
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php
index 21ce402..07f4da4 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php
@@ -177,7 +177,7 @@ function testNew() {
       'test_dependencies' => array(),
       'status' => TRUE,
       'uuid' => '30df59bd-7b03-4cf7-bb35-d42fc49f0651',
-      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->id,
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
       'dependencies' => array(),
       'protected_property' => '',
     );
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigLanguageOverrideWebTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigLanguageOverrideWebTest.php
index 34f5172..5ac458a 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigLanguageOverrideWebTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigLanguageOverrideWebTest.php
@@ -72,7 +72,7 @@ function testSiteNameTranslation() {
     $language_manager = \Drupal::languageManager()->reset();
     $this->assertTrue($language_manager->isMultilingual(), 'The test site is multilingual.');
     $language = \Drupal::languageManager()->getLanguage('xx');
-    $language->default = TRUE;
+    $language->setDefault(TRUE);
     language_save($language);
     language_delete('en');
     $this->assertFalse($language_manager->isMultilingual(), 'The test site is monolingual.');
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigOverridesPriorityTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigOverridesPriorityTest.php
index 6deab96..d294514 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigOverridesPriorityTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigOverridesPriorityTest.php
@@ -61,7 +61,7 @@ public function testOverridePriorities() {
     ));
     \Drupal::languageManager()->setConfigOverrideLanguage($language);
     \Drupal::languageManager()
-      ->getLanguageConfigOverride($language->id, 'system.site')
+      ->getLanguageConfigOverride($language->getId(), 'system.site')
       ->set('name', $language_overridden_name)
       ->set('mail', $language_overridden_mail)
       ->save();
diff --git a/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestAccessController.php b/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestAccessController.php
index cec5421..fee7966 100644
--- a/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestAccessController.php
+++ b/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestAccessController.php
@@ -10,7 +10,6 @@
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Entity\EntityAccessController;
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
 
 /**
  * Defines the access controller for the config_test entity type.
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationFormAccess.php b/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationFormAccess.php
index 10c5f25..da2d2bc 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationFormAccess.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationFormAccess.php
@@ -32,8 +32,8 @@ public function access(Route $route, Request $request, AccountInterface $account
       // that is logically not a good idea.
       $access =
         !empty($target_language) &&
-        !$target_language->locked &&
-        $target_language->id != $this->sourceLanguage->id;
+        !$target_language->isLocked() &&
+        $target_language->getId() != $this->sourceLanguage->getId();
 
       return $access ? static::ALLOW : static::DENY;
     }
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationOverviewAccess.php b/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationOverviewAccess.php
index 1eef1ff..868733a 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationOverviewAccess.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Access/ConfigTranslationOverviewAccess.php
@@ -69,7 +69,7 @@ public function access(Route $route, Request $request, AccountInterface $account
       $account->hasPermission('translate configuration') &&
       $mapper->hasSchema() &&
       $mapper->hasTranslatable() &&
-      !$this->sourceLanguage->locked;
+      !$this->sourceLanguage->isLocked();
 
     return $access ? static::ALLOW : static::DENY;
   }
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php b/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php
index 28fb744..d12e7d0 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\config_translation;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\Routing\RouteCollection;
 
@@ -269,14 +269,14 @@ public function hasTranslatable();
   /**
    * Checks whether there is already a translation for this mapper.
    *
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   A language object.
    *
    * @return bool
    *   TRUE if any of the configuration elements have a translation in the
    *   given language, FALSE otherwise.
    */
-  public function hasTranslation(Language $language);
+  public function hasTranslation(LanguageInterface $language);
 
   /**
    * Populate the config mapper with request data.
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php b/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php
index ce935f4..2e59b70 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Plugin\PluginBase;
 use Drupal\Core\Routing\RouteProviderInterface;
 use Drupal\Core\StringTranslation\TranslationInterface;
@@ -432,7 +433,7 @@ public function hasTranslatable() {
   /**
    * {@inheritdoc}
    */
-  public function hasTranslation(Language $language) {
+  public function hasTranslation(LanguageInterface $language) {
     foreach ($this->getConfigNames() as $name) {
       if ($this->localeConfigManager->hasTranslation($name, $language)) {
         return TRUE;
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Controller/ConfigTranslationController.php b/core/modules/config_translation/lib/Drupal/config_translation/Controller/ConfigTranslationController.php
index 827b99e..f7d4f14 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Controller/ConfigTranslationController.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Controller/ConfigTranslationController.php
@@ -152,7 +152,7 @@ public function itemPage(Request $request, $plugin_id) {
       '#header' => array($this->t('Language'), $this->t('Operations')),
     );
     foreach ($languages as $language) {
-      $langcode = $language->id;
+      $langcode = $language->getId();
 
       // This is needed because
       // ConfigMapperInterface::getAddRouteParameters(), for example,
@@ -163,7 +163,7 @@ public function itemPage(Request $request, $plugin_id) {
       // Prepare the language name and the operations depending on whether this
       // is the original language or not.
       if ($langcode == $original_langcode) {
-        $language_name = '<strong>' . $this->t('@language (original)', array('@language' => $language->name)) . '</strong>';
+        $language_name = '<strong>' . $this->t('@language (original)', array('@language' => $language->getName())) . '</strong>';
 
         // Check access for the path/route for editing, so we can decide to
         // include a link to edit or not.
@@ -189,7 +189,7 @@ public function itemPage(Request $request, $plugin_id) {
         }
       }
       else {
-        $language_name = $language->name;
+        $language_name = $language->getName();
 
         $operations = array();
         // If no translation exists for this language, link to add one.
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationAddForm.php b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationAddForm.php
index 9556be2..b7806d2 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationAddForm.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationAddForm.php
@@ -28,7 +28,7 @@ public function buildForm(array $form, array &$form_state, Request $request = NU
     $form = parent::buildForm($form, $form_state, $request, $plugin_id, $langcode);
     $form['#title'] = $this->t('Add @language translation for %label', array(
       '%label' => $this->mapper->getTitle(),
-      '@language' => $this->language->name,
+      '@language' => $this->language->getName(),
     ));
     return $form;
   }
@@ -38,7 +38,7 @@ public function buildForm(array $form, array &$form_state, Request $request = NU
    */
   public function submitForm(array &$form, array &$form_state) {
     parent::submitForm($form, $form_state);
-    drupal_set_message($this->t('Successfully saved @language translation.', array('@language' => $this->language->name)));
+    drupal_set_message($this->t('Successfully saved @language translation.', array('@language' => $this->language->getName())));
   }
 
 }
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationDeleteForm.php b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationDeleteForm.php
index f7f9b2e..cacebdf 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationDeleteForm.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationDeleteForm.php
@@ -87,7 +87,7 @@ public static function create(ContainerInterface $container) {
    * {@inheritdoc}
    */
   public function getQuestion() {
-    return $this->t('Are you sure you want to delete the @language translation of %label?', array('%label' => $this->mapper->getTitle(), '@language' => $this->language->name));
+    return $this->t('Are you sure you want to delete the @language translation of %label?', array('%label' => $this->mapper->getTitle(), '@language' => $this->language->getName()));
   }
 
   /**
@@ -137,7 +137,7 @@ public function buildForm(array $form, array &$form_state, Request $request = NU
    */
   public function submitForm(array &$form, array &$form_state) {
     foreach ($this->mapper->getConfigNames() as $name) {
-      $this->languageManager->getLanguageConfigOverride($this->language->id, $name)->delete();
+      $this->languageManager->getLanguageConfigOverride($this->language->getId(), $name)->delete();
     }
 
     // Flush all persistent caches.
@@ -146,7 +146,7 @@ public function submitForm(array &$form, array &$form_state) {
       $cache_backend->deleteAll();
     }
 
-    drupal_set_message($this->t('@language translation of %label was deleted', array('%label' => $this->mapper->getTitle(), '@language' => $this->language->name)));
+    drupal_set_message($this->t('@language translation of %label was deleted', array('%label' => $this->mapper->getTitle(), '@language' => $this->language->getName())));
 
     $form_state['redirect_route'] = array(
       'route_name' => $this->mapper->getOverviewRoute(),
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationEditForm.php b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationEditForm.php
index 565d07a..23c5a71 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationEditForm.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationEditForm.php
@@ -28,7 +28,7 @@ public function buildForm(array $form, array &$form_state, Request $request = NU
     $form = parent::buildForm($form, $form_state, $request, $plugin_id, $langcode);
     $form['#title'] = $this->t('Edit @language translation for %label', array(
       '%label' => $this->mapper->getTitle(),
-      '@language' => $this->language->name,
+      '@language' => $this->language->getName(),
     ));
     return $form;
   }
@@ -38,7 +38,7 @@ public function buildForm(array $form, array &$form_state, Request $request = NU
    */
   public function submitForm(array &$form, array &$form_state) {
     parent::submitForm($form, $form_state);
-    drupal_set_message($this->t('Successfully updated @language translation.', array('@language' => $this->language->name)));
+    drupal_set_message($this->t('Successfully updated @language translation.', array('@language' => $this->language->getName())));
   }
 
 }
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php
index fb3ba88..fa81fe4 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php
@@ -14,7 +14,7 @@
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Form\BaseFormIdInterface;
 use Drupal\Core\Form\FormBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 use Drupal\locale\StringStorageInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -224,7 +224,7 @@ public function submitForm(array &$form, array &$form_state) {
     foreach ($this->mapper->getConfigNames() as $name) {
       // Set configuration values based on form submission and source values.
       $base_config = $config_factory->get($name);
-      $config_translation = $this->languageManager->getLanguageConfigOverride($this->language->id, $name);
+      $config_translation = $this->languageManager->getLanguageConfigOverride($this->language->getId(), $name);
       $locations = $this->localeStorage->getLocations(array('type' => 'configuration', 'name' => $name));
 
       $this->setConfig($this->language, $base_config, $config_translation, $form_values[$name], !empty($locations));
@@ -324,12 +324,12 @@ protected function buildConfigForm(Element $schema, $config_data, $base_config_d
           '#theme' => 'config_translation_manage_form_element',
         );
         $build[$element_key]['source'] = array(
-          '#markup' => $base_config_data[$key] ? ('<span lang="' . $this->sourceLanguage->id . '">' . nl2br($base_config_data[$key] . '</span>')) : t('(Empty)'),
+          '#markup' => $base_config_data[$key] ? ('<span lang="' . $this->sourceLanguage->getId() . '">' . nl2br($base_config_data[$key] . '</span>')) : t('(Empty)'),
           '#title' => $this->t(
             '!label <span class="visually-hidden">(!source_language)</span>',
             array(
               '!label' => $this->t($definition['label']),
-              '!source_language' => $this->sourceLanguage->name,
+              '!source_language' => $this->sourceLanguage->getName(),
             )
           ),
           '#type' => 'item',
@@ -348,7 +348,7 @@ protected function buildConfigForm(Element $schema, $config_data, $base_config_d
   /**
    * Sets configuration based on a nested form value array.
    *
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   Set the configuration in this language.
    * @param \Drupal\Core\Config\Config $base_config
    *   Base configuration values, in the source language.
@@ -372,7 +372,7 @@ protected function buildConfigForm(Element $schema, $config_data, $base_config_d
    * @return array
    *   Translation configuration override data.
    */
-  protected function setConfig(Language $language, Config $base_config, Config $config_translation, array $config_values, $shipped_config = FALSE) {
+  protected function setConfig(LanguageInterface $language, Config $base_config, Config $config_translation, array $config_values, $shipped_config = FALSE) {
     foreach ($config_values as $key => $value) {
       if (is_array($value) && !isset($value['translation'])) {
         // Traverse into this level in the configuration.
@@ -388,7 +388,7 @@ protected function setConfig(Language $language, Config $base_config, Config $co
           // Get the translation for this original source string from locale.
           $conditions = array(
             'lid' => $source_string->lid,
-            'language' => $language->id,
+            'language' => $language->getId(),
           );
           $translations = $this->localeStorage->getTranslations($conditions + array('translated' => TRUE));
           // If we got a translation, take that, otherwise create a new one.
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/DateFormat.php b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/DateFormat.php
index 3abb57e..64f4d68 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/DateFormat.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/DateFormat.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Ajax\AjaxResponse;
 use Drupal\Core\Ajax\ReplaceCommand;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\StringTranslation\StringTranslationTrait;
 
 /**
@@ -22,7 +22,7 @@ class DateFormat implements ElementInterface {
   /**
    * {@inheritdoc}
    */
-  public function getFormElement(array $definition, Language $language, $value) {
+  public function getFormElement(array $definition, LanguageInterface $language, $value) {
     if (class_exists('intlDateFormatter')) {
       $description = $this->t('A user-defined date format. See the <a href="@url">PHP manual</a> for available options.', array('@url' => 'http://userguide.icu-project.org/formatparse/datetime'));
     }
@@ -32,10 +32,10 @@ public function getFormElement(array $definition, Language $language, $value) {
     $format = $this->t('Displayed as %date_format', array('%date_format' => \Drupal::service('date')->format(REQUEST_TIME, 'custom', $value)));
     return array(
       '#type' => 'textfield',
-      '#title' => $this->t($definition['label']) . '<span class="visually-hidden"> (' . $language->name . ')</span>',
+      '#title' => $this->t($definition['label']) . '<span class="visually-hidden"> (' . $language->getName() . ')</span>',
       '#description' => $description,
       '#default_value' => $value,
-      '#attributes' => array('lang' => $language->id),
+      '#attributes' => array('lang' => $language->getId()),
       '#field_suffix' => ' <div class="edit-date-format-suffix"><small id="edit-date-format-suffix">' . $format . '</small></div>',
       '#ajax' => array(
         'callback' => 'Drupal\config_translation\FormElement\DateFormat::ajaxSample',
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/ElementInterface.php b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/ElementInterface.php
index 9072cfc..ecc93f0 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/ElementInterface.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/ElementInterface.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\config_translation\FormElement;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Provides an interface for configuration translation form elements.
@@ -19,7 +19,7 @@
    *
    * @param array $definition
    *   Configuration schema type definition of the element.
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   Language object to display the translation form for.
    * @param string $value
    *   Default value for the form element.
@@ -27,6 +27,6 @@
    * @return array
    *   Form API array to represent the form element.
    */
-  public function getFormElement(array $definition, Language $language, $value);
+  public function getFormElement(array $definition, LanguageInterface $language, $value);
 
 }
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textarea.php b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textarea.php
index b796685..5f20e5c 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textarea.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textarea.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\config_translation\FormElement;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\StringTranslation\StringTranslationTrait;
 
 /**
@@ -19,7 +19,7 @@ class Textarea implements ElementInterface {
   /**
    * {@inheritdoc}
    */
-  public function getFormElement(array $definition, Language $language, $value) {
+  public function getFormElement(array $definition, LanguageInterface $language, $value) {
     // Estimate a comfortable size of the input textarea.
     $rows_words = ceil(str_word_count($value) / 5);
     $rows_newlines = substr_count($value, "\n" ) + 1;
@@ -28,9 +28,9 @@ public function getFormElement(array $definition, Language $language, $value) {
     return array(
       '#type' => 'textarea',
       '#default_value' => $value,
-      '#title' => $this->t($definition['label']) . '<span class="visually-hidden"> (' . $language->name . ')</span>',
+      '#title' => $this->t($definition['label']) . '<span class="visually-hidden"> (' . $language->getName() . ')</span>',
       '#rows' => $rows,
-      '#attributes' => array('lang' => $language->id),
+      '#attributes' => array('lang' => $language->getId()),
     );
   }
 
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textfield.php b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textfield.php
index 46d71fe..5905a7e 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textfield.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textfield.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\config_translation\FormElement;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\StringTranslation\StringTranslationTrait;
 
 /**
@@ -19,12 +19,12 @@ class Textfield implements ElementInterface {
   /**
    * {@inheritdoc}
    */
-  public function getFormElement(array $definition, Language $language, $value) {
+  public function getFormElement(array $definition, LanguageInterface $language, $value) {
     return array(
       '#type' => 'textfield',
       '#default_value' => $value,
-      '#title' => $this->t($definition['label']) . '<span class="visually-hidden"> (' . $language->name . ')</span>',
-      '#attributes' => array('lang' => $language->id),
+      '#title' => $this->t($definition['label']) . '<span class="visually-hidden"> (' . $language->getName() . ')</span>',
+      '#attributes' => array('lang' => $language->getId()),
     );
   }
 
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Tests/ConfigTranslationUiTest.php b/core/modules/config_translation/lib/Drupal/config_translation/Tests/ConfigTranslationUiTest.php
index 46ef47f..5f2989c 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Tests/ConfigTranslationUiTest.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Tests/ConfigTranslationUiTest.php
@@ -11,6 +11,7 @@
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Config\FileStorage;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -330,7 +331,7 @@ public function testContactConfigEntityTranslation() {
 
     // Test that delete links work and operations perform properly.
     foreach ($this->langcodes as $langcode) {
-      $replacements = array('%label' => t('!label !entity_type', array('!label' => $label, '!entity_type' => Unicode::strtolower(t('Contact category')))), '@language' => language_load($langcode)->name);
+      $replacements = array('%label' => t('!label !entity_type', array('!label' => $label, '!entity_type' => Unicode::strtolower(t('Contact category')))), '@language' => language_load($langcode)->getName());
 
       $this->drupalGet("$translation_base_url/$langcode/delete");
       $this->assertRaw(t('Are you sure you want to delete the @language translation of %label?', $replacements));
@@ -494,7 +495,7 @@ public function testSourceAndTargetLanguage() {
     $this->container
       ->get('config.factory')
       ->get('system.site')
-      ->set('langcode', Language::LANGCODE_NOT_SPECIFIED)
+      ->set('langcode', LanguageInterface::LANGCODE_NOT_SPECIFIED)
       ->save();
 
     // Make sure translation tab does not exist on the configuration page.
diff --git a/core/modules/config_translation/tests/Drupal/config_translation/Tests/ConfigMapperManagerTest.php b/core/modules/config_translation/tests/Drupal/config_translation/Tests/ConfigMapperManagerTest.php
index 860941b..dd51300 100644
--- a/core/modules/config_translation/tests/Drupal/config_translation/Tests/ConfigMapperManagerTest.php
+++ b/core/modules/config_translation/tests/Drupal/config_translation/Tests/ConfigMapperManagerTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\config_translation\ConfigMapperManager;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\TypedData\TypedDataInterface;
 use Drupal\Tests\UnitTestCase;
 
@@ -50,7 +51,7 @@ public function setUp() {
     $language_manager = $this->getMock('Drupal\Core\Language\LanguageManagerInterface');
     $language_manager->expects($this->once())
       ->method('getCurrentLanguage')
-      ->with(Language::TYPE_INTERFACE)
+      ->with(LanguageInterface::TYPE_INTERFACE)
       ->will($this->returnValue($language));
 
     $this->typedConfigManager = $this->getMockBuilder('Drupal\Core\Config\TypedConfigManager')
diff --git a/core/modules/contact/contact.install b/core/modules/contact/contact.install
index 477f359..5fc97bc 100644
--- a/core/modules/contact/contact.install
+++ b/core/modules/contact/contact.install
@@ -5,8 +5,6 @@
  * Install, update and uninstall functions for the contact module.
  */
 
-use Drupal\Core\Language\Language;
-
 /**
  * Implements hook_install().
  */
diff --git a/core/modules/contact/contact.module b/core/modules/contact/contact.module
index fe37a2b..f55d787 100644
--- a/core/modules/contact/contact.module
+++ b/core/modules/contact/contact.module
@@ -151,14 +151,14 @@ function contact_mail($key, &$message, $params) {
     $variables['!sender-url'] = $params['sender']->getEmail();
   }
 
-  $options = array('langcode' => $language->id);
+  $options = array('langcode' => $language->getId());
 
   switch ($key) {
     case 'page_mail':
     case 'page_copy':
       $message['subject'] .= t('[!category] !subject', $variables, $options);
       $message['body'][] = t("!sender-name (!sender-url) sent a message using the contact form at !form-url.", $variables, $options);
-      $build = entity_view($contact_message, 'mail', $language->id);
+      $build = entity_view($contact_message, 'mail', $language->getId());
       $message['body'][] = drupal_render($build);
       break;
 
@@ -177,7 +177,7 @@ function contact_mail($key, &$message, $params) {
       $message['body'][] = t('Hello !recipient-name,', $variables, $options);
       $message['body'][] = t("!sender-name (!sender-url) has sent you a message via your contact form at !site-name.", $variables, $options);
       $message['body'][] = t("If you don't want to receive such e-mails, you can change your settings at !recipient-edit-url.", $variables, $options);
-      $build = entity_view($contact_message, 'mail', $language->id);
+      $build = entity_view($contact_message, 'mail', $language->getId());
       $message['body'][] = drupal_render($build);
       break;
   }
diff --git a/core/modules/contact/lib/Drupal/contact/MessageForm.php b/core/modules/contact/lib/Drupal/contact/MessageForm.php
index 401291e..c5a3683 100644
--- a/core/modules/contact/lib/Drupal/contact/MessageForm.php
+++ b/core/modules/contact/lib/Drupal/contact/MessageForm.php
@@ -11,7 +11,6 @@
 use Drupal\Core\Entity\ContentEntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Flood\FloodInterface;
-use Drupal\Core\Language\Language;
 use Drupal\user\UserInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -200,7 +199,7 @@ public function save(array $form, array &$form_state) {
       $params['contact_category'] = $category;
 
       $to = implode(', ', $category->recipients);
-      $recipient_langcode = language_default()->id;
+      $recipient_langcode = language_default()->getId();
     }
     elseif ($recipient = $message->getPersonalRecipient()) {
       // Send to the user in the user's preferred language.
@@ -218,14 +217,14 @@ public function save(array $form, array &$form_state) {
 
     // If requested, send a copy to the user, using the current language.
     if ($message->copySender()) {
-      drupal_mail('contact', $key_prefix . '_copy', $sender->getEmail(), $language_interface->id, $params, $sender->getEmail());
+      drupal_mail('contact', $key_prefix . '_copy', $sender->getEmail(), $language_interface->getId(), $params, $sender->getEmail());
     }
 
     // If configured, send an auto-reply, using the current language.
     if (!$message->isPersonal() && $category->reply) {
       // User contact forms do not support an auto-reply message, so this
       // message always originates from the site.
-      drupal_mail('contact', 'page_autoreply', $sender->getEmail(), $language_interface->id, $params);
+      drupal_mail('contact', 'page_autoreply', $sender->getEmail(), $language_interface->getId(), $params);
     }
 
     $config = $this->config('contact.settings');
diff --git a/core/modules/contact/lib/Drupal/contact/Tests/ContactSitewideTest.php b/core/modules/contact/lib/Drupal/contact/Tests/ContactSitewideTest.php
index 7813678..583d650 100644
--- a/core/modules/contact/lib/Drupal/contact/Tests/ContactSitewideTest.php
+++ b/core/modules/contact/lib/Drupal/contact/Tests/ContactSitewideTest.php
@@ -124,7 +124,7 @@ function testSiteWideContact() {
 
     // Check that the category was created in site default language.
     $langcode = \Drupal::config('contact.category.' . $id)->get('langcode');
-    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
+    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
     $this->assertEqual($langcode, $default_langcode);
 
     // Make sure the newly created category is included in the list of categories.
diff --git a/core/modules/content_translation/content_translation.admin.inc b/core/modules/content_translation/content_translation.admin.inc
index eb03aea..9f018e9 100644
--- a/core/modules/content_translation/content_translation.admin.inc
+++ b/core/modules/content_translation/content_translation.admin.inc
@@ -7,7 +7,7 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Render\Element;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\field\FieldInstanceConfigInterface;
@@ -278,8 +278,8 @@ function content_translation_form_language_content_settings_validate(array $form
 
         $values = $bundle_settings['settings']['language'];
         if (empty($values['language_show']) && \Drupal::languageManager()->isLanguageLocked($values['langcode'])) {
-          foreach (\Drupal::languageManager()->getLanguages(Language::STATE_LOCKED) as $language) {
-            $locked_languages[] = $language->name;
+          foreach (\Drupal::languageManager()->getLanguages(LanguageInterface::STATE_LOCKED) as $language) {
+            $locked_languages[] = $language->getName();
           }
           form_set_error($name, $form_state, t('Translation is not supported if language is always one of: @locked_languages', array('@locked_languages' => implode(', ', $locked_languages))));
         }
diff --git a/core/modules/content_translation/content_translation.install b/core/modules/content_translation/content_translation.install
index f6dda75..383d043 100644
--- a/core/modules/content_translation/content_translation.install
+++ b/core/modules/content_translation/content_translation.install
@@ -6,7 +6,7 @@
  */
 
 use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
 
 /**
@@ -87,7 +87,7 @@ function content_translation_install() {
   // Assign a fairly low weight to ensure our implementation of
   // hook_module_implements_alter() is run among the last ones.
   module_set_weight('content_translation', 10);
-  \Drupal::service('language_negotiator')->saveConfiguration(Language::TYPE_CONTENT, array(LanguageNegotiationUrl::METHOD_ID => 0));
+  \Drupal::service('language_negotiator')->saveConfiguration(LanguageInterface::TYPE_CONTENT, array(LanguageNegotiationUrl::METHOD_ID => 0));
 
   $config_names = \Drupal::configFactory()->listAll('field.field.');
   foreach ($config_names as $name) {
diff --git a/core/modules/content_translation/content_translation.module b/core/modules/content_translation/content_translation.module
index 502d4e4..a7be087 100644
--- a/core/modules/content_translation/content_translation.module
+++ b/core/modules/content_translation/content_translation.module
@@ -11,7 +11,7 @@
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Field\FieldDefinition;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\TypedData\TranslatableInterface;
 use Drupal\field\Entity\FieldInstanceConfig;
@@ -72,8 +72,8 @@ function content_translation_module_implements_alter(&$implementations, $hook) {
 function content_translation_language_types_info_alter(array &$language_types) {
   // Make content language negotiation configurable by removing the 'locked'
   // flag.
-  $language_types[Language::TYPE_CONTENT]['locked'] = FALSE;
-  unset($language_types[Language::TYPE_CONTENT]['fixed']);
+  $language_types[LanguageInterface::TYPE_CONTENT]['locked'] = FALSE;
+  unset($language_types[LanguageInterface::TYPE_CONTENT]['fixed']);
 }
 
 /**
@@ -711,7 +711,7 @@ function content_translation_entity_presave(EntityInterface $entity) {
     // @todo Avoid using request attributes once translation metadata become
     //   regular fields.
     $attributes = \Drupal::request()->attributes;
-    \Drupal::service('content_translation.synchronizer')->synchronizeFields($entity, $entity->language()->id, $attributes->get('source_langcode'));
+    \Drupal::service('content_translation.synchronizer')->synchronizeFields($entity, $entity->language()->getId(), $attributes->get('source_langcode'));
   }
 }
 
@@ -792,8 +792,8 @@ function content_translation_language_configuration_element_validate($element, a
   $key = $form_state['content_translation']['key'];
   $values = $form_state['values'][$key];
   if (!$values['language_show'] && $values['content_translation'] && \Drupal::languageManager()->isLanguageLocked($values['langcode'])) {
-    foreach (\Drupal::languageManager()->getLanguages(Language::STATE_LOCKED) as $language) {
-      $locked_languages[] = $language->name;
+    foreach (\Drupal::languageManager()->getLanguages(LanguageInterface::STATE_LOCKED) as $language) {
+      $locked_languages[] = $language->getName();
     }
     // @todo Set the correct form element name as soon as the element parents
     //   are correctly set. We should be using NestedArray::getValue() but for
diff --git a/core/modules/content_translation/content_translation.pages.inc b/core/modules/content_translation/content_translation.pages.inc
index d4a7c48..3240fe9 100644
--- a/core/modules/content_translation/content_translation.pages.inc
+++ b/core/modules/content_translation/content_translation.pages.inc
@@ -5,7 +5,7 @@
  * The content translation user interface.
  */
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\ContentEntityInterface;
 
@@ -21,7 +21,7 @@
 function content_translation_overview(EntityInterface $entity) {
   $controller = content_translation_controller($entity->getEntityTypeId());
   $languages = \Drupal::languageManager()->getLanguages();
-  $original = $entity->getUntranslated()->language()->id;
+  $original = $entity->getUntranslated()->language()->getId();
   $translations = $entity->getTranslationLanguages();
   $administrator = \Drupal::currentUser()->hasPermission('administer languages');
 
@@ -50,8 +50,8 @@ function content_translation_overview(EntityInterface $entity) {
     $show_source_column = !empty($additional_source_langcodes);
 
     foreach ($languages as $language) {
-      $language_name = $language->name;
-      $langcode = $language->id;
+      $language_name = $language->getName();
+      $langcode = $language->getId();
 
       $add_path = $rel['drupal:content-translation-overview'] . '/add/' . $original . '/' . $langcode;
       $translate_path = $rel['drupal:content-translation-overview'] . '/edit/' . $langcode;
@@ -105,7 +105,7 @@ function content_translation_overview(EntityInterface $entity) {
           $source_name = t('n/a');
         }
         else {
-          $source_name = isset($languages[$source]) ? $languages[$source]->name : t('n/a');
+          $source_name = isset($languages[$source]) ? $languages[$source]->getName() : t('n/a');
           if ($controller->getTranslationAccess($entity, 'delete')) {
             $links['delete'] = isset($delete_links->links[$langcode]['href']) ? $delete_links->links[$langcode] : array('href' => $delete_links, 'language' => $language);
             $links['delete']['title'] = t('Delete');
@@ -115,7 +115,7 @@ function content_translation_overview(EntityInterface $entity) {
       else {
         // No such translation in the set yet: help user to create it.
         $row_title = $source_name = t('n/a');
-        $source = $entity->language()->id;
+        $source = $entity->language()->getId();
 
         if ($source != $langcode && $controller->getTranslationAccess($entity, 'create')) {
           if ($translatable) {
@@ -171,12 +171,13 @@ function content_translation_overview(EntityInterface $entity) {
  *   A renderable array of language switch links.
  */
 function _content_translation_get_switch_links($path) {
-  $links = \Drupal::languageManager()->getLanguageSwitchLinks(Language::TYPE_CONTENT, $path);
+  $links = \Drupal::languageManager()->getLanguageSwitchLinks(LanguageInterface::TYPE_CONTENT, $path);
   if (empty($links)) {
     // If content language is set up to fall back to the interface language,
-    // then there will be no switch links for Language::TYPE_CONTENT, ergo we
-    // also need to use interface switch links.
-    $links = \Drupal::languageManager()->getLanguageSwitchLinks(Language::TYPE_INTERFACE, $path);
+    // then there will be no switch links for
+    // \Drupal\Core\Language\LanguageInterface::TYPE_CONTENT, ergo we also need
+    // to use interface switch links.
+    $links = \Drupal::languageManager()->getLanguageSwitchLinks(LanguageInterface::TYPE_INTERFACE, $path);
   }
   return $links;
 }
@@ -186,10 +187,10 @@ function _content_translation_get_switch_links($path) {
  *
  * @param EntityInterface $entity
  *   The entity being translated.
- * @param Language $source
+ * @param \Drupal\Core\Language\LanguageInterface $source
  *   (optional) The language of the values being translated. Defaults to the
  *   entity language.
- * @param Language $target
+ * @param \Drupal\Core\Language\LanguageInterface $target
  *   (optional) The language of the translated values. Defaults to the current
  *   content language.
  *
@@ -199,12 +200,12 @@ function _content_translation_get_switch_links($path) {
  * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
  *   Use \Drupal\content_translation\Controller\ContentTranslationController::add().
  */
-function content_translation_add_page(EntityInterface $entity, Language $source = NULL, Language $target = NULL) {
+function content_translation_add_page(EntityInterface $entity, LanguageInterface $source = NULL, LanguageInterface $target = NULL) {
   $source = !empty($source) ? $source : $entity->language();
-  $target = !empty($target) ? $target : \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT);
+  $target = !empty($target) ? $target : \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
   // @todo Exploit the upcoming hook_entity_prepare() when available.
   content_translation_prepare_translation($entity, $source, $target);
-  $form_state['langcode'] = $target->id;
+  $form_state['langcode'] = $target->getId();
   $form_state['content_translation']['source'] = $source;
   $form_state['content_translation']['target'] = $target;
   $form_state['content_translation']['translation_form'] = !$entity->access('update');
@@ -216,7 +217,7 @@ function content_translation_add_page(EntityInterface $entity, Language $source
  *
  * @param \Drupal\Core\Entity\EntityInterface $entity
  *   The entity being translated.
- * @param \Drupal\Core\Language\Language $language
+ * @param \Drupal\Core\Language\LanguageInterface $language
  *   (optional) The language of the translated values. Defaults to the current
  *   content language.
  *
@@ -226,9 +227,9 @@ function content_translation_add_page(EntityInterface $entity, Language $source
  * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
  *   Use \Drupal\content_translation\Controller\ContentTranslationController::edit().
  */
-function content_translation_edit_page(EntityInterface $entity, Language $language = NULL) {
-  $language = !empty($language) ? $language : \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT);
-  $form_state['langcode'] = $language->id;
+function content_translation_edit_page(EntityInterface $entity, LanguageInterface $language = NULL) {
+  $language = !empty($language) ? $language : \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
+  $form_state['langcode'] = $language->getId();
   $form_state['content_translation']['translation_form'] = TRUE;
   return \Drupal::service('entity.form_builder')->getForm($entity, 'default', $form_state);
 }
@@ -238,14 +239,14 @@ function content_translation_edit_page(EntityInterface $entity, Language $langua
  *
  * @param \Drupal\Core\Entity\EntityInterface $entity
  *   The entitiy being translated.
- * @param \Drupal\Core\Language\Language $source
+ * @param \Drupal\Core\Language\LanguageInterface $source
  *   The language to be used as source.
- * @param \Drupal\Core\Language\Language $target
+ * @param \Drupal\Core\Language\LanguageInterface $target
  *   The language to be used as target.
  */
-function content_translation_prepare_translation(EntityInterface $entity, Language $source, Language $target) {
+function content_translation_prepare_translation(EntityInterface $entity, LanguageInterface $source, LanguageInterface $target) {
   if ($entity instanceof ContentEntityInterface) {
-    $source_translation = $entity->getTranslation($source->id);
-    $entity->addTranslation($target->id, $source_translation->toArray());
+    $source_translation = $entity->getTranslation($source->getId());
+    $entity->addTranslation($target->getId(), $source_translation->toArray());
   }
 }
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Access/ContentTranslationManageAccessCheck.php b/core/modules/content_translation/lib/Drupal/content_translation/Access/ContentTranslationManageAccessCheck.php
index b0e0fb6..9faa3b0 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Access/ContentTranslationManageAccessCheck.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Access/ContentTranslationManageAccessCheck.php
@@ -8,7 +8,7 @@
 namespace Drupal\content_translation\Access;
 
 use Drupal\Core\Entity\EntityManagerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Routing\Access\AccessInterface;
 use Drupal\Core\Session\AccountInterface;
 use Symfony\Component\Routing\Route;
@@ -70,20 +70,20 @@ public function access(Route $route, Request $request, AccountInterface $account
       switch ($operation) {
         case 'create':
           $source = language_load($source) ?: $entity->language();
-          $target = language_load($target) ?: \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT);
-          return ($source->id != $target->id
-            && isset($languages[$source->id])
-            && isset($languages[$target->id])
-            && !isset($translations[$target->id])
+          $target = language_load($target) ?: \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
+          return ($source->getId() != $target->getId()
+            && isset($languages[$source->getId()])
+            && isset($languages[$target->getId()])
+            && !isset($translations[$target->getId()])
             && $controller->getTranslationAccess($entity, $operation))
             ? static::ALLOW : static::DENY;
 
         case 'update':
         case 'delete':
-          $language = language_load($language) ?: \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT);
-          return isset($languages[$language->id])
-            && $language->id != $entity->getUntranslated()->language()->id
-            && isset($translations[$language->id])
+          $language = language_load($language) ?: \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
+          return isset($languages[$language->getId()])
+            && $language->getId() != $entity->getUntranslated()->language()->getId()
+            && isset($translations[$language->getId()])
             && $controller->getTranslationAccess($entity, $operation)
             ? static::ALLOW : static::DENY;
       }
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/ContentTranslationHandler.php b/core/modules/content_translation/lib/Drupal/content_translation/ContentTranslationHandler.php
index 76723c2..3cd1361 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/ContentTranslationHandler.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/ContentTranslationHandler.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Render\Element;
 
 /**
@@ -46,7 +46,7 @@ public function __construct(EntityTypeInterface $entity_type) {
    * {@inheritdoc}
    */
   public function retranslate(EntityInterface $entity, $langcode = NULL) {
-    $updated_langcode = !empty($langcode) ? $langcode : $entity->language()->id;
+    $updated_langcode = !empty($langcode) ? $langcode : $entity->language()->getId();
     $translations = $entity->getTranslationLanguages();
     foreach ($translations as $langcode => $language) {
       $entity->translation[$langcode]['outdated'] = $langcode != $updated_langcode;
@@ -73,7 +73,7 @@ public function getTranslationAccess(EntityInterface $entity, $op) {
    * {@inheritdoc}
    */
   public function getSourceLangcode(array $form_state) {
-    return isset($form_state['content_translation']['source']) ? $form_state['content_translation']['source']->id : FALSE;
+    return isset($form_state['content_translation']['source']) ? $form_state['content_translation']['source']->getId() : FALSE;
   }
 
   /**
@@ -82,7 +82,7 @@ public function getSourceLangcode(array $form_state) {
   public function entityFormAlter(array &$form, array &$form_state, EntityInterface $entity) {
     $form_controller = content_translation_form_controller($form_state);
     $form_langcode = $form_controller->getFormLangcode($form_state);
-    $entity_langcode = $entity->getUntranslated()->language()->id;
+    $entity_langcode = $entity->getUntranslated()->language()->getId();
     $source_langcode = $this->getSourceLangcode($form_state);
 
     $new_translation = !empty($source_langcode);
@@ -101,7 +101,7 @@ public function entityFormAlter(array &$form, array &$form_state, EntityInterfac
       $title = $this->entityFormTitle($entity);
       // When editing the original values display just the entity label.
       if ($form_langcode != $entity_langcode) {
-        $t_args = array('%language' => $languages[$form_langcode]->name, '%title' => $entity->label());
+        $t_args = array('%language' => $languages[$form_langcode]->getName(), '%title' => $entity->label());
         $title = empty($source_langcode) ? $title . ' [' . t('%language translation', $t_args) . ']' : t('Create %language translation of %title', $t_args);
       }
       $form['#title'] = $title;
@@ -112,7 +112,7 @@ public function entityFormAlter(array &$form, array &$form_state, EntityInterfac
     if ($has_translations && $new_translation) {
       $form['source_langcode'] = array(
         '#type' => 'details',
-        '#title' => t('Source language: @language', array('@language' => $languages[$source_langcode]->name)),
+        '#title' => t('Source language: @language', array('@language' => $languages[$source_langcode]->getName())),
         '#tree' => TRUE,
         '#weight' => -100,
         '#multilingual' => TRUE,
@@ -129,9 +129,9 @@ public function entityFormAlter(array &$form, array &$form_state, EntityInterfac
           '#submit' => array(array($this, 'entityFormSourceChange')),
         ),
       );
-      foreach (language_list(Language::STATE_CONFIGURABLE) as $language) {
-        if (isset($translations[$language->id])) {
-          $form['source_langcode']['source']['#options'][$language->id] = $language->name;
+      foreach (language_list(LanguageInterface::STATE_CONFIGURABLE) as $language) {
+        if (isset($translations[$language->getId()])) {
+          $form['source_langcode']['source']['#options'][$language->getId()] = $language->getName();
         }
       }
     }
@@ -142,9 +142,9 @@ public function entityFormAlter(array &$form, array &$form_state, EntityInterfac
     $language_widget = isset($form['langcode']) && $form['langcode']['#type'] == 'language_select';
     if ($language_widget && $has_translations) {
       $form['langcode']['#options'] = array();
-      foreach (language_list(Language::STATE_CONFIGURABLE) as $language) {
-        if (empty($translations[$language->id]) || $language->id == $entity_langcode) {
-          $form['langcode']['#options'][$language->id] = $language->name;
+      foreach (language_list(LanguageInterface::STATE_CONFIGURABLE) as $language) {
+        if (empty($translations[$language->getId()]) || $language->getId() == $entity_langcode) {
+          $form['langcode']['#options'][$language->getId()] = $language->getName();
         }
       }
     }
@@ -434,7 +434,7 @@ public function entityFormSourceChange($form, &$form_state) {
     $path = $entity->getSystemPath('drupal:content-translation-overview');
     $form_state['redirect'] = $path . '/add/' . $source . '/' . $form_controller->getFormLangcode($form_state);
     $languages = language_list();
-    drupal_set_message(t('Source language set to: %language', array('%language' => $languages[$source]->name)));
+    drupal_set_message(t('Source language set to: %language', array('%language' => $languages[$source]->getName())));
   }
 
   /**
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/FieldTranslationSynchronizer.php b/core/modules/content_translation/lib/Drupal/content_translation/FieldTranslationSynchronizer.php
index 196512b..544d1b7 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/FieldTranslationSynchronizer.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/FieldTranslationSynchronizer.php
@@ -50,7 +50,7 @@ public function synchronizeFields(ContentEntityInterface $entity, $sync_langcode
     // If the entity language is being changed there is nothing to synchronize.
     $entity_type = $entity->getEntityTypeId();
     $entity_unchanged = isset($entity->original) ? $entity->original : $this->entityManager->getStorage($entity_type)->loadUnchanged($entity->id());
-    if ($entity->getUntranslated()->language()->id != $entity_unchanged->getUntranslated()->language()->id) {
+    if ($entity->getUntranslated()->language()->getId() != $entity_unchanged->getUntranslated()->language()->getId()) {
       return;
     }
 
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Form/ContentTranslationDeleteForm.php b/core/modules/content_translation/lib/Drupal/content_translation/Form/ContentTranslationDeleteForm.php
index 92a544d..13e0e3f 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Form/ContentTranslationDeleteForm.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Form/ContentTranslationDeleteForm.php
@@ -55,7 +55,7 @@ public function getConfirmText() {
    * {@inheritdoc}
    */
   public function getQuestion() {
-    return $this->t('Are you sure you want to delete the @language translation of %label?', array('@language' => $this->language->name, '%label' => $this->entity->label()));
+    return $this->t('Are you sure you want to delete the @language translation of %label?', array('@language' => $this->language->getName(), '%label' => $this->entity->label()));
   }
 
   /**
@@ -75,14 +75,14 @@ public function getCancelRoute() {
    */
   public function submitForm(array &$form, array &$form_state) {
     // Remove the translated values.
-    $this->entity->removeTranslation($this->language->id);
+    $this->entity->removeTranslation($this->language->getId());
     $this->entity->save();
 
     // Remove any existing path alias for the removed translation.
     // @todo This should be taken care of by the Path module.
     if (\Drupal::moduleHandler()->moduleExists('path')) {
       $path = $this->entity->getSystemPath();
-      $conditions = array('source' => $path, 'langcode' => $this->language->id);
+      $conditions = array('source' => $path, 'langcode' => $this->language->getId());
       \Drupal::service('path.alias_storage')->delete($conditions);
     }
 
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSettingsTest.php b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSettingsTest.php
index 059cb79..664f553 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSettingsTest.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSettingsTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Language\Language;
 use Drupal\field\Entity\FieldConfig;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -76,7 +77,7 @@ function testSettingsUI() {
     // language is set as default and the language selector is hidden.
     $edit = array(
       'entity_types[comment]' => TRUE,
-      'settings[comment][node__comment_article][settings][language][langcode]' => Language::LANGCODE_NOT_SPECIFIED,
+      'settings[comment][node__comment_article][settings][language][langcode]' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'settings[comment][node__comment_article][settings][language][language_show]' => FALSE,
       'settings[comment][node__comment_article][translatable]' => TRUE,
       'settings[comment][node__comment_article][fields][comment_body]' => TRUE,
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncImageTest.php b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncImageTest.php
index 3f990db..5749baf 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncImageTest.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncImageTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\content_translation\Tests;
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
 
 /**
  * Tests the Content Translation image field synchronization capability.
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncUnitTest.php b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncUnitTest.php
index a1e0805..509287e 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncUnitTest.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationSyncUnitTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\content_translation\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\DrupalUnitTestBase;
 use Drupal\content_translation\FieldTranslationSynchronizer;
 
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationTestBase.php b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationTestBase.php
index cec9404..45cf888 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationTestBase.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationTestBase.php
@@ -103,7 +103,7 @@ protected function setupLanguages() {
     foreach ($this->langcodes as $langcode) {
       language_save(new Language(array('id' => $langcode)));
     }
-    array_unshift($this->langcodes, \Drupal::languageManager()->getDefaultLanguage()->id);
+    array_unshift($this->langcodes, \Drupal::languageManager()->getDefaultLanguage()->getId());
   }
 
   /**
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationUITest.php b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationUITest.php
index 12caf73..10b56cb 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationUITest.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationUITest.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\ContentEntityBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests the Content Translation UI.
@@ -251,7 +251,7 @@ protected function getNewEntityValues($langcode) {
    */
   protected function getEditValues($values, $langcode, $new = FALSE) {
     $edit = $values[$langcode];
-    $langcode = $new ? Language::LANGCODE_NOT_SPECIFIED : $langcode;
+    $langcode = $new ? LanguageInterface::LANGCODE_NOT_SPECIFIED : $langcode;
     foreach ($values[$langcode] as $property => $value) {
       if (is_array($value)) {
         $edit["{$property}[0][value]"] = $value[0]['value'];
diff --git a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationWorkflowsTest.php b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationWorkflowsTest.php
index 43e5d77..06674b8 100644
--- a/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationWorkflowsTest.php
+++ b/core/modules/content_translation/lib/Drupal/content_translation/Tests/ContentTranslationWorkflowsTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\content_translation\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\user\UserInterface;
 
 /**
@@ -183,7 +183,7 @@ protected function assertWorkflows(UserInterface $user, $expected_status) {
    * Assert that the current page does not contain shared form elements.
    */
   protected function assertNoSharedElements() {
-    $language_none = Language::LANGCODE_NOT_SPECIFIED;
+    $language_none = LanguageInterface::LANGCODE_NOT_SPECIFIED;
     return $this->assertNoFieldByXPath("//input[@name='field_test_text[$language_none][0][value]']", NULL, 'Shared elements are not available on the translation form.');
   }
 
diff --git a/core/modules/dblog/lib/Drupal/dblog/Tests/DbLogTest.php b/core/modules/dblog/lib/Drupal/dblog/Tests/DbLogTest.php
index 5b93c34..1807466 100644
--- a/core/modules/dblog/lib/Drupal/dblog/Tests/DbLogTest.php
+++ b/core/modules/dblog/lib/Drupal/dblog/Tests/DbLogTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\dblog\Tests;
 
 use Drupal\Component\Utility\Xss;
-use Drupal\Core\Language\Language;
 use Drupal\dblog\Controller\DbLogController;
 use Drupal\simpletest\WebTestBase;
 
diff --git a/core/modules/editor/lib/Drupal/editor/Tests/QuickEditIntegrationTest.php b/core/modules/editor/lib/Drupal/editor/Tests/QuickEditIntegrationTest.php
index 5f0c279..dcaf31d 100644
--- a/core/modules/editor/lib/Drupal/editor/Tests/QuickEditIntegrationTest.php
+++ b/core/modules/editor/lib/Drupal/editor/Tests/QuickEditIntegrationTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\editor\Tests;
 
 use Drupal\Component\Serialization\Json;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\quickedit\EditorSelector;
 use Drupal\quickedit\MetadataGenerator;
 use Drupal\quickedit\Plugin\InPlaceEditorManager;
@@ -119,7 +119,7 @@ public function setUp() {
    */
   protected function getSelectedEditor($entity_id, $field_name, $view_mode = 'default') {
     $entity = entity_load('entity_test', $entity_id, TRUE);
-    $items = $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get($field_name);
+    $items = $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get($field_name);
     $options = entity_get_display('entity_test', 'entity_test', $view_mode)->getComponent($field_name);
     return $this->editorSelector->getEditor($options['type'], $items);
   }
@@ -172,7 +172,7 @@ public function testMetadata() {
     $entity = entity_load('entity_test', $this->entity->id());
 
     // Verify metadata.
-    $items = $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get($this->field_name);
+    $items = $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get($this->field_name);
     $metadata = $this->metadataGenerator->generateFieldMetadata($items, 'default');
     $expected = array(
       'access' => TRUE,
@@ -212,7 +212,7 @@ public function testGetUntransformedTextCommand() {
     // Verify AJAX response.
     $controller = new EditorController();
     $request = new Request();
-    $response = $controller->getUntransformedText($entity, $this->field_name, Language::LANGCODE_NOT_SPECIFIED, 'default');
+    $response = $controller->getUntransformedText($entity, $this->field_name, LanguageInterface::LANGCODE_NOT_SPECIFIED, 'default');
     $expected = array(
       array(
         'command' => 'editorGetUntransformedText',
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php
index cc883c8..9c2420b 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAutoCreateTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\entity_reference\Tests;
 
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 
 /**
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceItemTest.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceItemTest.php
index 8c33d47..90e5a25 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceItemTest.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceItemTest.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FieldItemInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\field\Tests\FieldUnitTestBase;
 
 /**
@@ -58,14 +58,14 @@ public function setUp() {
     $this->vocabulary = entity_create('taxonomy_vocabulary', array(
       'name' => $this->randomName(),
       'vid' => drupal_strtolower($this->randomName()),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $this->vocabulary->save();
 
     $this->term = entity_create('taxonomy_term', array(
       'name' => $this->randomName(),
       'vid' => $this->vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $this->term->save();
 
@@ -106,7 +106,7 @@ public function testContentEntityReferenceItem() {
     $term2 = entity_create('taxonomy_term', array(
       'name' => $this->randomName(),
       'vid' => $this->term->bundle(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term2->save();
 
@@ -153,7 +153,7 @@ public function testConfigEntityReferenceItem() {
     $vocabulary2 = entity_create('taxonomy_vocabulary', array(
       'name' => $this->randomName(),
       'vid' => drupal_strtolower($this->randomName()),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $vocabulary2->save();
 
diff --git a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceSelectionAccessTest.php b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceSelectionAccessTest.php
index 19f5035..968e60c 100644
--- a/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceSelectionAccessTest.php
+++ b/core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceSelectionAccessTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\entity_reference\Tests;
 
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\comment\CommentInterface;
 use Drupal\simpletest\WebTestBase;
 
@@ -410,7 +410,7 @@ public function testCommentHandler() {
         'pid' => 0,
         'status' => CommentInterface::PUBLISHED,
         'subject' => 'Comment Published <&>',
-        'language' => Language::LANGCODE_NOT_SPECIFIED,
+        'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       ),
       'published_unpublished' => array(
         'entity_id' => $nodes['published']->id(),
@@ -421,7 +421,7 @@ public function testCommentHandler() {
         'pid' => 0,
         'status' => CommentInterface::NOT_PUBLISHED,
         'subject' => 'Comment Unpublished <&>',
-        'language' => Language::LANGCODE_NOT_SPECIFIED,
+        'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       ),
       'unpublished_published' => array(
         'entity_id' => $nodes['unpublished']->id(),
@@ -432,7 +432,7 @@ public function testCommentHandler() {
         'pid' => 0,
         'status' => CommentInterface::NOT_PUBLISHED,
         'subject' => 'Comment Published on Unpublished node <&>',
-        'language' => Language::LANGCODE_NOT_SPECIFIED,
+        'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       ),
     );
 
diff --git a/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php b/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php
index 6e19dad..bdfcc8f 100644
--- a/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php
+++ b/core/modules/field/lib/Drupal/field/Entity/FieldInstanceConfig.php
@@ -598,7 +598,7 @@ public function isMultiple() {
   public function getDefaultValue(EntityInterface $entity) {
     if (!empty($this->default_value_function)) {
       $function = $this->default_value_function;
-      return $function($entity, $this->getField(), $this, $entity->language()->id);
+      return $function($entity, $this->getField(), $this, $entity->language()->getId());
     }
     elseif (!empty($this->default_value)) {
       return $this->default_value;
diff --git a/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php b/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
index 84b587a..ae333fe 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
@@ -16,7 +16,7 @@
 use Drupal\Core\Entity\ContentEntityDatabaseStorage;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FormatterPluginManager;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\views\Views;
@@ -290,12 +290,12 @@ public function query($use_groupby = FALSE) {
       $field = $field_definition;
       if ($field->isTranslatable() && !empty($this->view->display_handler->options['field_langcode_add_to_query'])) {
         $column = $this->tableAlias . '.langcode';
-        // By the same reason as field_language the field might be Language::LANGCODE_NOT_SPECIFIED in reality so allow it as well.
+        // By the same reason as field_language the field might be LanguageInterface::LANGCODE_NOT_SPECIFIED in reality so allow it as well.
         // @see this::field_langcode()
-        $default_langcode = language_default()->id;
+        $default_langcode = language_default()->getId();
         $langcode = str_replace(
           array('***CURRENT_LANGUAGE***', '***DEFAULT_LANGUAGE***'),
-          array($this->languageManager->getCurrentLanguage(Language::TYPE_CONTENT), $default_langcode),
+          array($this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT), $default_langcode),
           $this->view->display_handler->options['field_langcode']
         );
         $placeholder = $this->placeholder();
@@ -900,24 +900,24 @@ protected function addSelfTokens(&$tokens, $item) {
    */
   function field_langcode(EntityInterface $entity) {
     if ($this->getFieldDefinition()->isTranslatable()) {
-      $default_langcode = language_default()->id;
+      $default_langcode = language_default()->getId();
       $langcode = str_replace(
         array('***CURRENT_LANGUAGE***', '***DEFAULT_LANGUAGE***'),
-        array($this->languageManager->getCurrentLanguage(Language::TYPE_CONTENT), $default_langcode),
+        array($this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT), $default_langcode),
         $this->view->display_handler->options['field_language']
       );
 
       // Give the Entity Field API a chance to fallback to a different language
-      // (or Language::LANGCODE_NOT_SPECIFIED), in case the field has no data
+      // (or LanguageInterface::LANGCODE_NOT_SPECIFIED), in case the field has no data
       // for the selected language. FieldItemListInterface::view() does this as
       // well, but since the returned language code is used before calling it,
       // the fallback needs to happen explicitly.
-      $langcode = $this->entityManager->getTranslationFromContext($entity, $langcode)->language()->id;
+      $langcode = $this->entityManager->getTranslationFromContext($entity, $langcode)->language()->getId();
 
       return $langcode;
     }
     else {
-      return Language::LANGCODE_NOT_SPECIFIED;
+      return LanguageInterface::LANGCODE_NOT_SPECIFIED;
     }
   }
 
diff --git a/core/modules/field/lib/Drupal/field/Tests/DisplayApiTest.php b/core/modules/field/lib/Drupal/field/Tests/DisplayApiTest.php
index 3a31e00..9a9ed1e 100644
--- a/core/modules/field/lib/Drupal/field/Tests/DisplayApiTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/DisplayApiTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\field\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests the field display API.
@@ -149,7 +149,7 @@ function testFieldItemListView() {
     $setting = $display['settings']['test_formatter_setting_multiple'];
     $this->assertNoText($this->label, 'Label was not displayed.');
     $this->assertText('field_test_entity_display_build_alter', 'Alter fired, display passed.');
-    $this->assertText('entity language is ' . Language::LANGCODE_NOT_SPECIFIED, 'Language is placed onto the context.');
+    $this->assertText('entity language is ' . LanguageInterface::LANGCODE_NOT_SPECIFIED, 'Language is placed onto the context.');
     $array = array();
     foreach ($this->values as $delta => $value) {
       $array[] = $delta . ':' . $value['value'];
diff --git a/core/modules/field/lib/Drupal/field/Tests/FieldAttachOtherTest.php b/core/modules/field/lib/Drupal/field/Tests/FieldAttachOtherTest.php
index 39f6e28..696021b 100644
--- a/core/modules/field/lib/Drupal/field/Tests/FieldAttachOtherTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/FieldAttachOtherTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\field\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Unit test class for non-storage related field_attach_* functions.
@@ -180,7 +180,7 @@ function testEntityDisplayViewMultiple() {
   function testFieldAttachCache() {
     // Initialize random values and a test entity.
     $entity_init = entity_create('entity_test', array('type' => $this->instance->bundle));
-    $langcode = Language::LANGCODE_NOT_SPECIFIED;
+    $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
     $values = $this->_generateTestFieldValues($this->field->getCardinality());
 
     // Non-cacheable entity type.
diff --git a/core/modules/field/lib/Drupal/field/Tests/FieldInfoTest.php b/core/modules/field/lib/Drupal/field/Tests/FieldInfoTest.php
index c97a481..369645c 100644
--- a/core/modules/field/lib/Drupal/field/Tests/FieldInfoTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/FieldInfoTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\field\Tests;
 
-use Drupal\Core\Language\Language;
 
 /**
  * Tests field information for fields, instances, and bundles.
diff --git a/core/modules/field/lib/Drupal/field/Tests/FieldTestBase.php b/core/modules/field/lib/Drupal/field/Tests/FieldTestBase.php
index 3f5d2c5..e105c05 100644
--- a/core/modules/field/lib/Drupal/field/Tests/FieldTestBase.php
+++ b/core/modules/field/lib/Drupal/field/Tests/FieldTestBase.php
@@ -8,7 +8,7 @@
 namespace Drupal\field\Tests;
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -46,11 +46,11 @@ function _generateTestFieldValues($cardinality) {
    *   The array of expected values.
    * @param $langcode
    *   (Optional) The language code for the values. Defaults to
-   *   Drupal\Core\Language\Language::LANGCODE_NOT_SPECIFIED.
+   *   Drupal\Core\Language\LanguageInterface::LANGCODE_NOT_SPECIFIED.
    * @param $column
    *   (Optional) The name of the column to check. Defaults to 'value'.
    */
-  function assertFieldValues(EntityInterface $entity, $field_name, $expected_values, $langcode = Language::LANGCODE_NOT_SPECIFIED, $column = 'value') {
+  function assertFieldValues(EntityInterface $entity, $field_name, $expected_values, $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED, $column = 'value') {
     // Re-load the entity to make sure we have the latest changes.
     entity_get_controller($entity->getEntityTypeId())->resetCache(array($entity->id()));
     $e = entity_load($entity->getEntityTypeId(), $entity->id());
diff --git a/core/modules/field/lib/Drupal/field/Tests/FieldUnitTestBase.php b/core/modules/field/lib/Drupal/field/Tests/FieldUnitTestBase.php
index 5717a23..b94c256 100644
--- a/core/modules/field/lib/Drupal/field/Tests/FieldUnitTestBase.php
+++ b/core/modules/field/lib/Drupal/field/Tests/FieldUnitTestBase.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\DrupalUnitTestBase;
 
 /**
@@ -145,11 +145,11 @@ function _generateTestFieldValues($cardinality) {
    *   The array of expected values.
    * @param $langcode
    *   (Optional) The language code for the values. Defaults to
-   *   Drupal\Core\Language\Language::LANGCODE_NOT_SPECIFIED.
+   *   Drupal\Core\Language\LanguageInterface::LANGCODE_NOT_SPECIFIED.
    * @param $column
    *   (Optional) The name of the column to check. Defaults to 'value'.
    */
-  function assertFieldValues(EntityInterface $entity, $field_name, $expected_values, $langcode = Language::LANGCODE_NOT_SPECIFIED, $column = 'value') {
+  function assertFieldValues(EntityInterface $entity, $field_name, $expected_values, $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED, $column = 'value') {
     // Re-load the entity to make sure we have the latest changes.
     entity_get_controller($entity->getEntityTypeId())->resetCache(array($entity->id()));
     $e = entity_load($entity->getEntityTypeId(), $entity->id());
diff --git a/core/modules/field/lib/Drupal/field/Tests/TranslationTest.php b/core/modules/field/lib/Drupal/field/Tests/TranslationTest.php
index 89af9c9..2f23729 100644
--- a/core/modules/field/lib/Drupal/field/Tests/TranslationTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/TranslationTest.php
@@ -176,7 +176,7 @@ function testTranslatableFieldSaveLoad() {
 
     // @todo Test every translation once the Entity Translation API allows for
     //   multilingual defaults.
-    $langcode = $entity->language()->id;
+    $langcode = $entity->language()->getId();
     $this->assertEqual($entity->getTranslation($langcode)->{$field_name_default}->getValue(), $instance->default_value, format_string('Default value correctly populated for language %language.', array('%language' => $langcode)));
 
     // Check that explicit empty values are not overridden with default values.
diff --git a/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php b/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php
index 9a25836..bb1274e 100644
--- a/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/Views/HandlerFieldFieldTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\field\Tests\Views;
 
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
 use Drupal\views\ViewExecutable;
 use Drupal\views\Views;
 
diff --git a/core/modules/field/tests/modules/field_test/field_test.module b/core/modules/field/tests/modules/field_test/field_test.module
index 45a0c0d..b0f3a6c 100644
--- a/core/modules/field/tests/modules/field_test/field_test.module
+++ b/core/modules/field/tests/modules/field_test/field_test.module
@@ -108,7 +108,7 @@ function field_test_entity_display_build_alter(&$output, $context) {
   }
 
   if (isset($output['test_field'])) {
-    $output['test_field'][] = array('#markup' => 'entity language is ' . $context['entity']->language()->id);
+    $output['test_field'][] = array('#markup' => 'entity language is ' . $context['entity']->language()->getId());
   }
 }
 
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Tests/FieldUiTestBase.php b/core/modules/field_ui/lib/Drupal/field_ui/Tests/FieldUiTestBase.php
index f103e6d..3e54cea 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Tests/FieldUiTestBase.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Tests/FieldUiTestBase.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\field_ui\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -39,7 +39,7 @@ function setUp() {
       'name' => $this->randomName(),
       'description' => $this->randomName(),
       'vid' => drupal_strtolower($this->randomName()),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'help' => '',
       'nodes' => array('article' => 'article'),
       'weight' => mt_rand(0, 10),
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php
index 212df05..306c4c4 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Tests/ManageFieldsTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\field_ui\Tests;
 
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Component\Utility\String;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\field\Entity\FieldInstanceConfig;
@@ -42,7 +42,7 @@ function setUp() {
     $vocabulary = entity_create('taxonomy_vocabulary', array(
       'name' => 'Tags',
       'vid' => 'tags',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $vocabulary->save();
 
diff --git a/core/modules/file/lib/Drupal/file/Entity/File.php b/core/modules/file/lib/Drupal/file/Entity/File.php
index 39f27d6..26416d6 100644
--- a/core/modules/file/lib/Drupal/file/Entity/File.php
+++ b/core/modules/file/lib/Drupal/file/Entity/File.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Field\FieldDefinition;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\file\FileInterface;
 use Drupal\user\UserInterface;
 
@@ -43,7 +43,7 @@ class File extends ContentEntityBase implements FileInterface {
    * @var array
    */
   protected $values = array(
-    'langcode' => array(Language::LANGCODE_DEFAULT => array(0 => array('value' => Language::LANGCODE_NOT_SPECIFIED))),
+    'langcode' => array(LanguageInterface::LANGCODE_DEFAULT => array(0 => array('value' => LanguageInterface::LANGCODE_NOT_SPECIFIED))),
   );
 
   /**
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileFieldPathTest.php b/core/modules/file/lib/Drupal/file/Tests/FileFieldPathTest.php
index 3366b2b..b9134d3 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileFieldPathTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileFieldPathTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\file\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests that files are uploaded to proper locations.
  */
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileFieldRSSContentTest.php b/core/modules/file/lib/Drupal/file/Tests/FileFieldRSSContentTest.php
index ba46dc6..5b75862 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileFieldRSSContentTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileFieldRSSContentTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\file\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests that formatters are working properly.
  */
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileFieldRevisionTest.php b/core/modules/file/lib/Drupal/file/Tests/FileFieldRevisionTest.php
index 070217b..ed06571 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileFieldRevisionTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileFieldRevisionTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\file\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests file handling with node revisions.
  */
diff --git a/core/modules/file/lib/Drupal/file/Tests/FilePrivateTest.php b/core/modules/file/lib/Drupal/file/Tests/FilePrivateTest.php
index afb0114..3dce48e 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FilePrivateTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FilePrivateTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\file\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests file access on private nodes.
  */
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileTokenReplaceTest.php b/core/modules/file/lib/Drupal/file/Tests/FileTokenReplaceTest.php
index 35bb593..69ec082 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileTokenReplaceTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileTokenReplaceTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\file\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests the file token replacement in strings.
  */
@@ -53,10 +51,10 @@ function testFileTokenReplacement() {
     $tests['[file:mime]'] = check_plain($file->getMimeType());
     $tests['[file:size]'] = format_size($file->getSize());
     $tests['[file:url]'] = check_plain(file_create_url($file->getFileUri()));
-    $tests['[file:created]'] = format_date($file->getCreatedTime(), 'medium', '', NULL, $language_interface->id);
-    $tests['[file:created:short]'] = format_date($file->getCreatedTime(), 'short', '', NULL, $language_interface->id);
-    $tests['[file:changed]'] = format_date($file->getChangedTime(), 'medium', '', NULL, $language_interface->id);
-    $tests['[file:changed:short]'] = format_date($file->getChangedTime(), 'short', '', NULL, $language_interface->id);
+    $tests['[file:created]'] = format_date($file->getCreatedTime(), 'medium', '', NULL, $language_interface->getId());
+    $tests['[file:created:short]'] = format_date($file->getCreatedTime(), 'short', '', NULL, $language_interface->getId());
+    $tests['[file:changed]'] = format_date($file->getChangedTime(), 'medium', '', NULL, $language_interface->getId());
+    $tests['[file:changed:short]'] = format_date($file->getChangedTime(), 'short', '', NULL, $language_interface->getId());
     $tests['[file:owner]'] = check_plain(user_format_name($this->admin_user));
     $tests['[file:owner:uid]'] = $file->getOwnerId();
 
@@ -64,7 +62,7 @@ function testFileTokenReplacement() {
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('file' => $file), array('langcode' => $language_interface->id));
+      $output = $token_service->replace($input, array('file' => $file), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Sanitized file token %token replaced.', array('%token' => $input)));
     }
 
@@ -75,7 +73,7 @@ function testFileTokenReplacement() {
     $tests['[file:size]'] = format_size($file->getSize());
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('file' => $file), array('langcode' => $language_interface->id, 'sanitize' => FALSE));
+      $output = $token_service->replace($input, array('file' => $file), array('langcode' => $language_interface->getId(), 'sanitize' => FALSE));
       $this->assertEqual($output, $expected, format_string('Unsanitized file token %token replaced.', array('%token' => $input)));
     }
   }
diff --git a/core/modules/file/lib/Drupal/file/Tests/SaveTest.php b/core/modules/file/lib/Drupal/file/Tests/SaveTest.php
index 50d6847..daa4048 100644
--- a/core/modules/file/lib/Drupal/file/Tests/SaveTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/SaveTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\file\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests saving files.
@@ -46,7 +46,7 @@ function testFileSave() {
     $this->assertEqual($loaded_file->isPermanent(), $file->isPermanent(), 'Status was saved correctly.');
     $this->assertEqual($file->getSize(), filesize($file->getFileUri()), 'File size was set correctly.', 'File');
     $this->assertTrue($file->getChangedTime() > 1, 'File size was set correctly.', 'File');
-    $this->assertEqual($loaded_file->langcode->value, Language::LANGCODE_NOT_SPECIFIED, 'Langcode was defaulted correctly.');
+    $this->assertEqual($loaded_file->langcode->value, LanguageInterface::LANGCODE_NOT_SPECIFIED, 'Langcode was defaulted correctly.');
 
     // Resave the file, updating the existing record.
     file_test_reset();
diff --git a/core/modules/filter/filter.module b/core/modules/filter/filter.module
index 3efe9ad..6af6efe 100644
--- a/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -9,7 +9,6 @@
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Template\Attribute;
@@ -147,13 +146,13 @@ function filter_formats(AccountInterface $account = NULL) {
   // All available formats are cached for performance.
   if (!isset($formats['all'])) {
     $language_interface = \Drupal::languageManager()->getCurrentLanguage();
-    if ($cache = \Drupal::cache()->get("filter_formats:{$language_interface->id}")) {
+    if ($cache = \Drupal::cache()->get("filter_formats:{$language_interface->getId()}")) {
       $formats['all'] = $cache->data;
     }
     else {
       $formats['all'] = \Drupal::entityManager()->getStorage('filter_format')->loadByProperties(array('status' => TRUE));
       uasort($formats['all'], 'Drupal\Core\Config\Entity\ConfigEntityBase::sort');
-      \Drupal::cache()->set("filter_formats:{$language_interface->id}", $formats['all'], Cache::PERMANENT, array('filter_formats' => TRUE));
+      \Drupal::cache()->set("filter_formats:{$language_interface->getId()}", $formats['all'], Cache::PERMANENT, array('filter_formats' => TRUE));
     }
   }
 
diff --git a/core/modules/filter/lib/Drupal/filter/FilterPluginManager.php b/core/modules/filter/lib/Drupal/filter/FilterPluginManager.php
index 2be9e4a..54e1c4e 100644
--- a/core/modules/filter/lib/Drupal/filter/FilterPluginManager.php
+++ b/core/modules/filter/lib/Drupal/filter/FilterPluginManager.php
@@ -10,7 +10,6 @@
 use Drupal\Component\Plugin\PluginManagerBase;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\Core\Plugin\DefaultPluginManager;
 use Drupal\Core\Plugin\Discovery\AlterDecorator;
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php
index 041f309..6f153a6 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterCrudTest.php
@@ -84,7 +84,7 @@ function testTextFormatCrud() {
    */
   function verifyTextFormat($format) {
     $t_args = array('%format' => $format->name);
-    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
+    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
 
     // Verify the loaded filter has all properties.
     $filter_format = entity_load('filter_format', $format->format);
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php
index 6321c1b..cb98907 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterSecurityTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\filter\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 use Drupal\filter\Plugin\FilterInterface;
 
diff --git a/core/modules/forum/lib/Drupal/forum/Tests/ForumTest.php b/core/modules/forum/lib/Drupal/forum/Tests/ForumTest.php
index 6217835..4063d8a 100644
--- a/core/modules/forum/lib/Drupal/forum/Tests/ForumTest.php
+++ b/core/modules/forum/lib/Drupal/forum/Tests/ForumTest.php
@@ -300,7 +300,7 @@ private function doAdminTests($user) {
       'name' => 'Tags',
       'description' => $description,
       'vid' => 'tags',
-      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->id,
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
       'help' => $help,
     ));
     $vocabulary->save();
diff --git a/core/modules/forum/lib/Drupal/forum/Tests/ForumUninstallTest.php b/core/modules/forum/lib/Drupal/forum/Tests/ForumUninstallTest.php
index 130143f..cd695c0 100644
--- a/core/modules/forum/lib/Drupal/forum/Tests/ForumUninstallTest.php
+++ b/core/modules/forum/lib/Drupal/forum/Tests/ForumUninstallTest.php
@@ -43,7 +43,7 @@ function testForumUninstallWithField() {
     // Create a taxonomy term.
     $term = entity_create('taxonomy_term', array(
       'name' => t('A term'),
-      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->id,
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
       'description' => '',
       'parent' => array(0),
       'vid' => 'forums',
diff --git a/core/modules/hal/lib/Drupal/hal/Normalizer/ContentEntityNormalizer.php b/core/modules/hal/lib/Drupal/hal/Normalizer/ContentEntityNormalizer.php
index f374fa3..d433656 100644
--- a/core/modules/hal/lib/Drupal/hal/Normalizer/ContentEntityNormalizer.php
+++ b/core/modules/hal/lib/Drupal/hal/Normalizer/ContentEntityNormalizer.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\rest\LinkManager\LinkManagerInterface;
 use Symfony\Component\Serializer\Exception\UnexpectedValueException;
 
@@ -136,7 +136,7 @@ public function denormalize($data, $class, $format = NULL, array $context = arra
       $langcode = language_get_default_langcode($typed_data_ids['entity_type'], $typed_data_ids['bundle']);
     }
     else {
-      $langcode = Language::LANGCODE_NOT_SPECIFIED;
+      $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
     }
 
     $entity_type = $this->entityManager->getDefinition($typed_data_ids['entity_type']);
diff --git a/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php b/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php
index 99a669c..d898815 100644
--- a/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php
+++ b/core/modules/hal/lib/Drupal/hal/Normalizer/FieldNormalizer.php
@@ -26,9 +26,11 @@ class FieldNormalizer extends NormalizerBase {
    * Implements \Symfony\Component\Serializer\Normalizer\NormalizerInterface::normalize()
    */
   public function normalize($field, $format = NULL, array $context = array()) {
+    /** @var \Drupal\Core\Field\FieldItemInterface $field */
     $normalized_field_items = array();
 
     // Get the field definition.
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
     $entity = $field->getEntity();
     $field_name = $field->getName();
     $field_definition = $field->getFieldDefinition();
@@ -43,8 +45,8 @@ public function normalize($field, $format = NULL, array $context = array()) {
     // to the field item values.
     else {
       foreach ($entity->getTranslationLanguages() as $language) {
-        $context['langcode'] = $language->id;
-        $translation = $entity->getTranslation($language->id);
+        $context['langcode'] = $language->getId();
+        $translation = $entity->getTranslation($language->getId());
         $translated_field = $translation->get($field_name);
         $normalized_field_items = array_merge($normalized_field_items, $this->normalizeFieldItems($translated_field, $format, $context));
       }
diff --git a/core/modules/language/language.module b/core/modules/language/language.module
index f35da4d..efbf47d 100644
--- a/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -6,7 +6,7 @@
  */
 
 use Drupal\Core\PhpStorage\PhpStorageFactory;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\ConfigurableLanguageManager;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 use Drupal\language\Entity\Language as LanguageEntity;
@@ -148,7 +148,7 @@ function language_element_info_alter(&$type) {
     $type['language_select']['#process'] = array_merge($type['language_select']['#process'], array('language_process_language_select', 'form_process_select', 'ajax_process_form'));
     $type['language_select']['#theme'] = 'select';
     $type['language_select']['#theme_wrappers'] = array_merge($type['language_select']['#theme_wrappers'], array('form_element'));
-    $type['language_select']['#languages'] = Language::STATE_CONFIGURABLE;
+    $type['language_select']['#languages'] = LanguageInterface::STATE_CONFIGURABLE;
     $type['language_select']['#multiple'] = FALSE;
   }
 }
@@ -168,7 +168,7 @@ function language_process_language_select($element) {
   if (!isset($element['#options'])) {
     $element['#options'] = array();
     foreach (\Drupal::languageManager()->getLanguages($element['#languages']) as $langcode => $language) {
-      $element['#options'][$langcode] = $language->locked ? t('- @name -', array('@name' => $language->name)) : $language->name;
+      $element['#options'][$langcode] = $language->isLocked() ? t('- @name -', array('@name' => $language->getName())) : $language->getName();
     }
   }
   // Add "Built-in English" language to the select when the default value is
@@ -209,14 +209,14 @@ function language_element_info() {
  */
 function language_configuration_element_default_options() {
   $language_options = array(
-    'site_default' => t("Site's default language (!language)", array('!language' => \Drupal::languageManager()->getDefaultLanguage()->name)),
+    'site_default' => t("Site's default language (!language)", array('!language' => \Drupal::languageManager()->getDefaultLanguage()->getName())),
     'current_interface' => t('Current interface language'),
     'authors_default' => t("Author's preferred language"),
   );
 
-  $languages = \Drupal::languageManager()->getLanguages(Language::STATE_ALL);
+  $languages = \Drupal::languageManager()->getLanguages(LanguageInterface::STATE_ALL);
   foreach ($languages as $langcode => $language) {
-    $language_options[$langcode] = $language->locked ? t('- @name -', array('@name' => $language->name)) : $language->name;
+    $language_options[$langcode] = $language->isLocked() ? t('- @name -', array('@name' => $language->getName())) : $language->getName();
   }
 
   return $language_options;
@@ -389,11 +389,11 @@ function language_get_default_langcode($entity_type, $bundle) {
   $language_interface = \Drupal::languageManager()->getCurrentLanguage();
   switch ($configuration['langcode']) {
     case 'site_default':
-      $default_value = \Drupal::languageManager()->getDefaultLanguage()->id;
+      $default_value = \Drupal::languageManager()->getDefaultLanguage()->getId();
       break;
 
     case 'current_interface':
-      $default_value = $language_interface->id;
+      $default_value = $language_interface->getId();
       break;
 
     case 'authors_default':
@@ -403,7 +403,7 @@ function language_get_default_langcode($entity_type, $bundle) {
         $default_value = $language_code;
       }
       else {
-        $default_value = $language_interface->id;
+        $default_value = $language_interface->getId();
       }
       break;
   }
@@ -419,28 +419,28 @@ function language_get_default_langcode($entity_type, $bundle) {
 /**
  * API function to add or update a language.
  *
- * @param $language
+ * @param \Drupal\Core\Language\LanguageInterface $language
  *   Language object with properties corresponding to the 'language'
  *   configuration properties.
  */
-function language_save($language) {
-  $language_entity = entity_load('language_entity', $language->id);
+function language_save(LanguageInterface $language) {
+  $language_entity = entity_load('language_entity', $language->getId());
   if (!$language_entity) {
     $language_entity = entity_create('language_entity', array(
-      'id' => $language->id,
+      'id' => $language->getId(),
     ));
   }
   $language->is_new = $language_entity->isNew();
 
   // Assign language properties to language entity.
-  $language_entity->label = isset($language->name) ? $language->name : '';
-  $language_entity->direction = isset($language->direction) ? $language->direction : '0';
-  $language_entity->locked = !empty($language->locked);
-  $language_entity->weight = isset($language->weight) ? $language->weight : 0;
-  $language_entity->setDefault(!empty($language->default));
+  $language_entity->label = $language->getName();
+  $language_entity->direction = $language->getDirection();
+  $language_entity->locked = $language->isLocked();
+  $language_entity->weight = $language->getWeight();
+  $language_entity->setDefault($language->isDefault());
   $language_entity->save();
-  $t_args = array('%language' => $language->name, '%langcode' => $language->id);
-  if ($language->is_new) {
+  $t_args = array('%language' => $language->getName(), '%langcode' => $language->getId());
+  if ($language_entity->isNew()) {
     watchdog('language', 'The %language (%langcode) language has been created.', $t_args);
   }
   else {
@@ -460,12 +460,12 @@ function language_save($language) {
  *   TRUE if language is successfully deleted. Otherwise FALSE.
  */
 function language_delete($langcode) {
-  $languages = \Drupal::languageManager()->getLanguages(Language::STATE_ALL);
-  if (isset($languages[$langcode]) && !$languages[$langcode]->locked) {
+  $languages = \Drupal::languageManager()->getLanguages(LanguageInterface::STATE_ALL);
+  if (isset($languages[$langcode]) && !$languages[$langcode]->isLocked()) {
     $language = $languages[$langcode];
 
     // Remove the language.
-    entity_delete_multiple('language_entity', array($language->id));
+    entity_delete_multiple('language_entity', array($language->getId()));
 
     $language_manager = \Drupal::languageManager();
     $language_manager->reset();
@@ -479,7 +479,7 @@ function language_delete($langcode) {
       ConfigurableLanguageManager::rebuildServices();
     }
 
-    $t_args = array('%language' => $language->name, '%langcode' => $language->id);
+    $t_args = array('%language' => $language->getName(), '%langcode' => $language->getId());
     watchdog('language', 'The %language (%langcode) language has been removed.', $t_args);
     return TRUE;
   }
@@ -502,18 +502,18 @@ function language_delete($langcode) {
  */
 function language_language_types_info() {
   return array(
-    Language::TYPE_INTERFACE => array(
+    LanguageInterface::TYPE_INTERFACE => array(
       'name' => t('User interface text'),
       'description' => t('Order of language detection methods for user interface text. If a translation of user interface text is available in the detected language, it will be displayed.'),
       'locked' => TRUE,
     ),
-    Language::TYPE_CONTENT => array(
+    LanguageInterface::TYPE_CONTENT => array(
       'name' => t('Content'),
       'description' => t('Order of language detection methods for content. If a version of content is available in the detected language, it will be displayed.'),
       'fixed' => array(LanguageNegotiationUI::METHOD_ID),
       'locked' => TRUE,
     ),
-    Language::TYPE_URL => array(
+    LanguageInterface::TYPE_URL => array(
       'fixed' => array(LanguageNegotiationUrl::METHOD_ID, LanguageNegotiationUrlFallback::METHOD_ID),
       'locked' => TRUE,
     ),
@@ -535,10 +535,10 @@ function language_negotiation_url_prefixes_update() {
   foreach (\Drupal::languageManager()->getLanguages() as $language) {
     // The prefix for this language should be updated if it's not assigned yet
     // or the prefix is set to the empty string.
-    if (empty($prefixes[$language->id])) {
+    if (empty($prefixes[$language->getId()])) {
       // For the default language, set the prefix to the empty string,
       // otherwise use the langcode.
-      $prefixes[$language->id] = !empty($language->default) ? '' : $language->id;
+      $prefixes[$language->getId()] = $language->isDefault() ? '' : $language->getId();
     }
     // Otherwise we keep the configured prefix.
   }
@@ -663,12 +663,12 @@ function language_form_system_regional_settings_alter(&$form, &$form_state) {
   $languages = \Drupal::languageManager()->getLanguages();
   $default = \Drupal::languageManager()->getDefaultLanguage();
   foreach ($languages as $key => $language) {
-    $language_options[$key] = $language->name;
+    $language_options[$key] = $language->getName();
   }
   $form['locale']['site_default_language'] = array(
     '#type' => 'select',
     '#title' => t('Default language'),
-    '#default_value' => $default->id,
+    '#default_value' => $default->getId(),
     '#options' => $language_options,
     '#description' => t('It is not recommended to change the default language on a working site. <a href="@language-detection">Configure the Selected language</a> setting on the detection and selection page to change the fallback language for language selection.', array('@language-detection' => url('admin/config/regional/language/detection'))),
     '#weight' => -1,
@@ -685,6 +685,6 @@ function language_form_system_regional_settings_alter(&$form, &$form_state) {
 function language_system_regional_settings_form_submit($form, &$form_state) {
   $languages = \Drupal::languageManager()->getLanguages();
   $language = $languages[$form_state['values']['site_default_language']];
-  $language->default = TRUE;
+  $language->setDefault(TRUE);
   language_save($language);
 }
diff --git a/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
index bfadec0..983283b 100644
--- a/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
+++ b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Config\Config;
 use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\Config\TypedConfigManagerInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageDefault;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 
@@ -73,7 +73,7 @@ public function loadOverrides($names) {
       $data = $this->storage->readMultiple(array_values($language_names));
       // Re-key the data array to use configuration names rather than override
       // names.
-      $prefix_length = strlen(static::LANGUAGE_CONFIG_PREFIX . '.' . $this->language->id) + 1;
+      $prefix_length = strlen(static::LANGUAGE_CONFIG_PREFIX . '.' . $this->language->getId()) + 1;
       foreach ($data as $key => $value) {
         unset($data[$key]);
         $key = substr($key, $prefix_length);
@@ -109,7 +109,7 @@ protected function getLanguageConfigNames(array $names) {
     $language_names = array();
     if (isset($this->language)) {
       foreach ($names as $name) {
-        if ($language_name = $this->getLanguageConfigName($this->language->id, $name)) {
+        if ($language_name = $this->getLanguageConfigName($this->language->getId(), $name)) {
           $language_names[$name] = $language_name;
         }
       }
@@ -139,7 +139,7 @@ protected function getLanguageConfigName($langcode, $name) {
    * {@inheritdoc}
    */
   public function getCacheSuffix() {
-    return $this->language ? $this->language->id : NULL;
+    return $this->language ? $this->language->getId() : NULL;
   }
 
   /**
@@ -152,7 +152,7 @@ public function getLanguage() {
   /**
    * {@inheritdoc}
    */
-  public function setLanguage(Language $language = NULL) {
+  public function setLanguage(LanguageInterface $language = NULL) {
     $this->language = $language;
     return $this;
   }
diff --git a/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php
index 1c3de55..81b2e39 100644
--- a/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php
+++ b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverrideInterface.php
@@ -8,7 +8,7 @@
 namespace Drupal\language\Config;
 
 use Drupal\Core\Config\ConfigFactoryOverrideInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageDefault;
 
 /**
@@ -32,12 +32,12 @@ public function getLanguage();
   /**
    * Sets the language to be used in configuration overrides.
    *
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   The language object used to override configuration data.
    *
    * @return $this
    */
-  public function setLanguage(Language $language = NULL);
+  public function setLanguage(LanguageInterface $language = NULL);
 
   /**
    * Sets the language to be used in configuration overrides from the default.
diff --git a/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
index 101449c..e34c126 100644
--- a/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
+++ b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\language;
 
+use Drupal\Core\Language\LanguageInterface as CoreLanguageInterface;
 use Drupal\Core\PhpStorage\PhpStorageFactory;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
@@ -135,7 +136,7 @@ public function init() {
    * {@inheritdoc}
    */
   public function isMultilingual() {
-    return count($this->getLanguages(Language::STATE_CONFIGURABLE)) > 1;
+    return count($this->getLanguages(CoreLanguageInterface::STATE_CONFIGURABLE)) > 1;
   }
 
   /**
@@ -197,7 +198,7 @@ public function saveLanguageTypesConfiguration(array $values) {
   /**
    * {@inheritdoc}
    */
-  public function getCurrentLanguage($type = Language::TYPE_INTERFACE) {
+  public function getCurrentLanguage($type = CoreLanguageInterface::TYPE_INTERFACE) {
     if (!isset($this->negotiatedLanguages[$type])) {
       // Ensure we have a valid value for this language type.
       $this->negotiatedLanguages[$type] = $this->getDefaultLanguage();
@@ -214,8 +215,8 @@ public function getCurrentLanguage($type = Language::TYPE_INTERFACE) {
         // original strings which can be translated by calling them again
         // afterwards. This can happen for instance while parsing negotiation
         // method definitions.
-        elseif ($type == Language::TYPE_INTERFACE) {
-          return new Language(array('id' => Language::LANGCODE_SYSTEM));
+        elseif ($type == CoreLanguageInterface::TYPE_INTERFACE) {
+          return new Language(array('id' => CoreLanguageInterface::LANGCODE_SYSTEM));
         }
       }
     }
@@ -269,12 +270,12 @@ public function setNegotiator(LanguageNegotiatorInterface $negotiator) {
   /**
    * {@inheritdoc}
    */
-  public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
+  public function getLanguages($flags = CoreLanguageInterface::STATE_CONFIGURABLE) {
     if (!isset($this->languages)) {
       // Prepopulate the language list with the default language to keep things
       // working even if we have no configuration.
       $default = $this->getDefaultLanguage();
-      $this->languages = array($default->id => $default);
+      $this->languages = array($default->getId() => $default);
 
       // Retrieve the config storage to list available languages.
       $prefix = 'language.entity.';
@@ -287,17 +288,17 @@ public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
         $langcode = $data['id'];
         // Initialize default property so callers have an easy reference and can
         // save the same object without data loss.
-        $data['default'] = ($langcode == $default->id);
+        $data['default'] = ($langcode == $default->getId());
         $data['name'] = $data['label'];
         $this->languages[$langcode] = new Language($data);
-        $weight = max(array($weight, $this->languages[$langcode]->weight));
+        $weight = max(array($weight, $this->languages[$langcode]->getWeight()));
       }
 
       // Add locked languages, they will be filtered later if needed.
       $this->languages += $this->getDefaultLockedLanguages($weight);
 
       // Sort the language list by weight then title.
-      Language::sort($this->languages);
+      uasort($this->languages, '\Drupal\Core\Language\Language::sort');
     }
 
     return parent::getLanguages($flags);
@@ -310,15 +311,15 @@ public function updateLockedLanguageWeights() {
     $max_weight = 0;
 
     // Get maximum weight to update the system languages to keep them on bottom.
-    foreach ($this->getLanguages(Language::STATE_CONFIGURABLE) as $language) {
-      if (!$language->locked && $language->weight > $max_weight) {
-        $max_weight = $language->weight;
+    foreach ($this->getLanguages(CoreLanguageInterface::STATE_CONFIGURABLE) as $language) {
+      if (!$language->isLocked() && $language->getWeight() > $max_weight) {
+        $max_weight = $language->getWeight();
       }
     }
 
     // Loop locked languages to maintain the existing order.
-    $locked_languages = $this->getLanguages(Language::STATE_LOCKED);
-    $config_ids = array_map(function($language) { return 'language.entity.' . $language->id; }, $locked_languages);
+    $locked_languages = $this->getLanguages(CoreLanguageInterface::STATE_LOCKED);
+    $config_ids = array_map(function(CoreLanguageInterface $language) { return 'language.entity.' . $language->getId(); }, $locked_languages);
     foreach ($this->configFactory->loadMultiple($config_ids) as $config_id => $config) {
       // Update system languages weight.
       $max_weight++;
@@ -332,10 +333,10 @@ public function updateLockedLanguageWeights() {
    */
   public function getFallbackCandidates($langcode = NULL, array $context = array()) {
     if ($this->isMultilingual()) {
-      // Get languages ordered by weight, add Language::LANGCODE_NOT_SPECIFIED
+      // Get languages ordered by weight, add LanguageInterface::LANGCODE_NOT_SPECIFIED
       // at the end.
       $candidates = array_keys($this->getLanguages());
-      $candidates[] = Language::LANGCODE_NOT_SPECIFIED;
+      $candidates[] = CoreLanguageInterface::LANGCODE_NOT_SPECIFIED;
       $candidates = array_combine($candidates, $candidates);
 
       // The first candidate should always be the desired language if specified.
@@ -388,7 +389,7 @@ public function getLanguageSwitchLinks($type, $path) {
   /**
    * {@inheritdoc}
    */
-  public function setConfigOverrideLanguage(Language $language = NULL) {
+  public function setConfigOverrideLanguage(CoreLanguageInterface $language = NULL) {
     $this->configFactoryOverride->setLanguage($language);
     return $this;
   }
diff --git a/core/modules/language/lib/Drupal/language/ConfigurableLanguageManagerInterface.php b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManagerInterface.php
index 9bbf2ce..8c34c1b 100644
--- a/core/modules/language/lib/Drupal/language/ConfigurableLanguageManagerInterface.php
+++ b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManagerInterface.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\language;
 
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Symfony\Component\HttpFoundation\Request;
 
diff --git a/core/modules/language/lib/Drupal/language/Entity/Language.php b/core/modules/language/lib/Drupal/language/Entity/Language.php
index 8a2f9fe..d77d576 100644
--- a/core/modules/language/lib/Drupal/language/Entity/Language.php
+++ b/core/modules/language/lib/Drupal/language/Entity/Language.php
@@ -87,9 +87,9 @@ class Language extends ConfigEntityBase implements LanguageInterface {
    * container using the language.default service in when the entity is saved.
    * The value is set correctly when a language entity is created or loaded.
    *
-   * @see \Drupal\language\Entity\Language::postSave()
-   * @see \Drupal\language\Entity\Language::isDefault()
-   * @see \Drupal\language\Entity\Language::setDefault()
+   * @see \Drupal\language\Entity\LanguageInterface::postSave()
+   * @see \Drupal\language\Entity\LanguageInterface::isDefault()
+   * @see \Drupal\language\Entity\LanguageInterface::setDefault()
    *
    * @var bool
    */
@@ -101,8 +101,8 @@ class Language extends ConfigEntityBase implements LanguageInterface {
    * This property is not saved to the language entity, but is needed for
    * detecting when to rebuild the services.
    *
-   * @see \Drupal\language\Entity\Language::preSave()
-   * @see \Drupal\language\Entity\Language::postSave()
+   * @see \Drupal\language\Entity\LanguageInterface::preSave()
+   * @see \Drupal\language\Entity\LanguageInterface::postSave()
    *
    * @var bool
    */
@@ -137,7 +137,7 @@ public function preSave(EntityStorageInterface $storage) {
     parent::preSave($storage);
     // Store whether or not the site is already multilingual so that we can
     // rebuild services if necessary during
-    // \Drupal\language\Entity\Language::postSave().
+    // \Drupal\language\Entity\LanguageInterface::postSave().
     $this->preSaveMultilingual = \Drupal::languageManager()->isMultilingual();
     // Languages are picked from a predefined list which is given in English.
     // For the uncommon case of custom languages the label should be given in
diff --git a/core/modules/language/lib/Drupal/language/EventSubscriber/LanguageRequestSubscriber.php b/core/modules/language/lib/Drupal/language/EventSubscriber/LanguageRequestSubscriber.php
index 7700611..fcbd232 100644
--- a/core/modules/language/lib/Drupal/language/EventSubscriber/LanguageRequestSubscriber.php
+++ b/core/modules/language/lib/Drupal/language/EventSubscriber/LanguageRequestSubscriber.php
@@ -86,7 +86,7 @@ public function onKernelRequestLanguage(GetResponseEvent $event) {
       }
       // After the language manager has initialized, set the default langcode
       // for the string translations.
-      $langcode = $this->languageManager->getCurrentLanguage()->id;
+      $langcode = $this->languageManager->getCurrentLanguage()->getId();
       $this->translation->setDefaultLangcode($langcode);
     }
   }
diff --git a/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php b/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php
index 3eb0bc6..1f74246 100644
--- a/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php
@@ -98,7 +98,7 @@ public function submitForm(array &$form, array &$form_state) {
     // Save the language and inform the user that it happened.
     $language = language_save($language);
 
-    drupal_set_message($this->t('The language %language has been created and can now be used.', array('%language' => $language->name)));
+    drupal_set_message($this->t('The language %language has been created and can now be used.', array('%language' => $language->getName())));
 
     // Tell the user they have the option to add a language switcher block
     // to their theme so they can switch between the languages.
@@ -124,7 +124,7 @@ public function validateCustom(array $form, array &$form_state) {
       $this->validateCommon($form['custom_language'], $form_state);
 
       if ($language = language_load($langcode)) {
-        $this->setFormError('langcode', $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->name, '%langcode' => $langcode)));
+        $this->setFormError('langcode', $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->getName(), '%langcode' => $langcode)));
       }
     }
     else {
@@ -142,7 +142,7 @@ public function validatePredefined($form, &$form_state) {
     }
     else {
       if ($language = language_load($langcode)) {
-        $this->setFormError('predefined_langcode', $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->name, '%langcode' => $langcode)));
+        $this->setFormError('predefined_langcode', $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->getName(), '%langcode' => $langcode)));
       }
     }
   }
diff --git a/core/modules/language/lib/Drupal/language/Form/LanguageDeleteForm.php b/core/modules/language/lib/Drupal/language/Form/LanguageDeleteForm.php
index 241bbe7..6edb8aa 100644
--- a/core/modules/language/lib/Drupal/language/Form/LanguageDeleteForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/LanguageDeleteForm.php
@@ -89,7 +89,7 @@ public function buildForm(array $form, array &$form_state) {
     $langcode = $this->entity->id();
 
     // Warn and redirect user when attempting to delete the default language.
-    if (language_default()->id == $langcode) {
+    if (language_default()->getId() == $langcode) {
       drupal_set_message($this->t('The default language cannot be deleted.'));
       $url = $this->urlGenerator->generateFromPath('admin/config/regional/language', array('absolute' => TRUE));
       return new RedirectResponse($url);
diff --git a/core/modules/language/lib/Drupal/language/Form/LanguageEditForm.php b/core/modules/language/lib/Drupal/language/Form/LanguageEditForm.php
index 2dacdc2..9c69bb8 100644
--- a/core/modules/language/lib/Drupal/language/Form/LanguageEditForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/LanguageEditForm.php
@@ -51,8 +51,8 @@ public function submitForm(array &$form, array &$form_state) {
     $languages = language_list();
     $langcode = $form_state['values']['langcode'];
     $language = $languages[$langcode];
-    $language->name = $form_state['values']['name'];
-    $language->direction = $form_state['values']['direction'];
+    $language->setName($form_state['values']['name']);
+    $language->setDirection($form_state['values']['direction']);
     language_save($language);
 
     $form_state['redirect_route']['route_name'] = 'language.admin_overview';
diff --git a/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php b/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php
index d3719bc..583787a 100644
--- a/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php
+++ b/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Core\Entity\EntityForm;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -85,8 +85,8 @@ public function commonForm(array &$form) {
       '#description' => $this->t('Direction that text in this language is presented.'),
       '#default_value' => $language->direction,
       '#options' => array(
-        Language::DIRECTION_LTR => $this->t('Left to right'),
-        Language::DIRECTION_RTL => $this->t('Right to left'),
+        LanguageInterface::DIRECTION_LTR => $this->t('Left to right'),
+        LanguageInterface::DIRECTION_RTL => $this->t('Right to left'),
       ),
     );
 
diff --git a/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php b/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php
index f82e54a..3dc4ad7 100644
--- a/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php
@@ -63,7 +63,7 @@ public function buildForm(array $form, array &$form_state) {
 
     $existing_languages = array();
     foreach ($languages as $langcode => $language) {
-      $existing_languages[$langcode] = $language->name;
+      $existing_languages[$langcode] = $language->getName();
     }
 
     // If we have no languages available, present the list of predefined languages
diff --git a/core/modules/language/lib/Drupal/language/Form/NegotiationSelectedForm.php b/core/modules/language/lib/Drupal/language/Form/NegotiationSelectedForm.php
index 14c13f4..47d61eb 100644
--- a/core/modules/language/lib/Drupal/language/Form/NegotiationSelectedForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/NegotiationSelectedForm.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\language\Form;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Form\ConfigFormBase;
 
 /**
@@ -30,7 +30,7 @@ public function buildForm(array $form, array &$form_state) {
     $form['selected_langcode'] = array(
       '#type' => 'language_select',
       '#title' => t('Language'),
-      '#languages' => Language::STATE_CONFIGURABLE | Language::STATE_SITE_DEFAULT,
+      '#languages' => LanguageInterface::STATE_CONFIGURABLE | LanguageInterface::STATE_SITE_DEFAULT,
       '#default_value' => $config->get('selected_langcode'),
     );
 
diff --git a/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php b/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php
index d8c2490..bfec4ac 100644
--- a/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php
@@ -72,17 +72,17 @@ public function buildForm(array $form, array &$form_state) {
     $prefixes = language_negotiation_url_prefixes();
     $domains = language_negotiation_url_domains();
     foreach ($languages as $langcode => $language) {
-      $t_args = array('%language' => $language->name, '%langcode' => $language->id);
+      $t_args = array('%language' => $language->getName(), '%langcode' => $language->getId());
       $form['prefix'][$langcode] = array(
         '#type' => 'textfield',
-        '#title' => $language->default ? t('%language (%langcode) path prefix (Default language)', $t_args) : t('%language (%langcode) path prefix', $t_args),
+        '#title' => $language->isDefault() ? t('%language (%langcode) path prefix (Default language)', $t_args) : t('%language (%langcode) path prefix', $t_args),
         '#maxlength' => 64,
         '#default_value' => isset($prefixes[$langcode]) ? $prefixes[$langcode] : '',
         '#field_prefix' => $base_url . '/',
       );
       $form['domain'][$langcode] = array(
         '#type' => 'textfield',
-        '#title' => t('%language (%langcode) domain', array('%language' => $language->name, '%langcode' => $language->id)),
+        '#title' => t('%language (%langcode) domain', array('%language' => $language->getName(), '%langcode' => $language->getId())),
         '#maxlength' => 128,
         '#default_value' => isset($domains[$langcode]) ? $domains[$langcode] : '',
       );
@@ -105,7 +105,7 @@ public function validateForm(array &$form, array &$form_state) {
       $value = $form_state['values']['prefix'][$langcode];
 
       if ($value === '') {
-        if (!$language->default && $form_state['values']['language_negotiation_url_part'] == LanguageNegotiationUrl::CONFIG_PATH_PREFIX) {
+        if (!$language->isDefault() && $form_state['values']['language_negotiation_url_part'] == LanguageNegotiationUrl::CONFIG_PATH_PREFIX) {
           // Throw a form error if the prefix is blank for a non-default language,
           // although it is required for selected negotiation type.
           $this->setFormError("prefix][$langcode", $form_state, t('The prefix may only be left blank for the default language.'));
@@ -119,7 +119,7 @@ public function validateForm(array &$form, array &$form_state) {
       elseif (isset($count[$value]) && $count[$value] > 1) {
         // Throw a form error if there are two languages with the same
         // domain/prefix.
-        $this->setFormError("prefix][$langcode", $form_state, t('The prefix for %language, %value, is not unique.', array('%language' => $language->name, '%value' => $value)));
+        $this->setFormError("prefix][$langcode", $form_state, t('The prefix for %language, %value, is not unique.', array('%language' => $language->getName(), '%value' => $value)));
       }
     }
 
@@ -129,7 +129,7 @@ public function validateForm(array &$form, array &$form_state) {
       $value = $form_state['values']['domain'][$langcode];
 
       if ($value === '') {
-        if (!$language->default && $form_state['values']['language_negotiation_url_part'] == LanguageNegotiationUrl::CONFIG_DOMAIN) {
+        if (!$language->isDefault() && $form_state['values']['language_negotiation_url_part'] == LanguageNegotiationUrl::CONFIG_DOMAIN) {
           // Throw a form error if the domain is blank for a non-default language,
           // although it is required for selected negotiation type.
           $this->setFormError("domain][$langcode", $form_state, t('The domain may only be left blank for the default language.'));
@@ -138,7 +138,7 @@ public function validateForm(array &$form, array &$form_state) {
       elseif (isset($count[$value]) && $count[$value] > 1) {
         // Throw a form error if there are two languages with the same
         // domain/domain.
-        $this->setFormError("domain][$langcode", $form_state, t('The domain for %language, %value, is not unique.', array('%language' => $language->name, '%value' => $value)));
+        $this->setFormError("domain][$langcode", $form_state, t('The domain for %language, %value, is not unique.', array('%language' => $language->getName(), '%value' => $value)));
       }
     }
 
diff --git a/core/modules/language/lib/Drupal/language/LanguageAccessController.php b/core/modules/language/lib/Drupal/language/LanguageAccessController.php
index 2cc17d0..5ebded0 100644
--- a/core/modules/language/lib/Drupal/language/LanguageAccessController.php
+++ b/core/modules/language/lib/Drupal/language/LanguageAccessController.php
@@ -9,7 +9,6 @@
 
 use Drupal\Core\Entity\EntityAccessController;
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Session\AccountInterface;
 
 class LanguageAccessController extends EntityAccessController {
diff --git a/core/modules/language/lib/Drupal/language/LanguageListBuilder.php b/core/modules/language/lib/Drupal/language/LanguageListBuilder.php
index c5bd66a..36209c5 100644
--- a/core/modules/language/lib/Drupal/language/LanguageListBuilder.php
+++ b/core/modules/language/lib/Drupal/language/LanguageListBuilder.php
@@ -49,7 +49,7 @@ public function getDefaultOperations(EntityInterface $entity) {
     $default = language_default();
 
     // Deleting the site default language is not allowed.
-    if ($entity->id() == $default->id) {
+    if ($entity->id() == $default->getId()) {
       unset($operations['delete']);
     }
 
diff --git a/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodBase.php b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodBase.php
index 9ed0f7c..a10924b 100644
--- a/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodBase.php
+++ b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodBase.php
@@ -8,7 +8,7 @@
 namespace Drupal\language;
 
 use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface as CoreLanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 
 /**
@@ -61,9 +61,9 @@ public function setCurrentUser(AccountInterface $current_user) {
   /**
    * {@inheritdoc}
    */
-  public function persist(Language $language) {
+  public function persist(CoreLanguageInterface $language) {
     // Remember the method ID used to detect the language.
-    $language->method_id = static::METHOD_ID;
+    $language->setNegotiationMethodId(static::METHOD_ID);
   }
 
 }
diff --git a/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodInterface.php b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodInterface.php
index fefa585..bffe23a 100644
--- a/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodInterface.php
+++ b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodInterface.php
@@ -8,7 +8,7 @@
 namespace Drupal\language;
 
 use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface as CoreLanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -57,9 +57,9 @@ public function getLangcode(Request $request = NULL);
   /**
    * Notifies the plugin that the language code it returned has been accepted.
    *
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   The accepted language.
    */
-  public function persist(Language $language);
+  public function persist(CoreLanguageInterface $language);
 
 }
diff --git a/core/modules/language/lib/Drupal/language/LanguageNegotiator.php b/core/modules/language/lib/Drupal/language/LanguageNegotiator.php
index ec924e3..d567c54 100644
--- a/core/modules/language/lib/Drupal/language/LanguageNegotiator.php
+++ b/core/modules/language/lib/Drupal/language/LanguageNegotiator.php
@@ -159,7 +159,7 @@ public function initializeType($type) {
     if (!$language) {
       // If no other language was found use the default one.
       $language = $this->languageManager->getDefaultLanguage();
-      $language->method_id = LanguageNegotiatorInterface::METHOD_ID;
+      $language->setNegotiationMethodId(LanguageNegotiatorInterface::METHOD_ID);
     }
 
     return $language;
diff --git a/core/modules/language/lib/Drupal/language/LanguageNegotiatorInterface.php b/core/modules/language/lib/Drupal/language/LanguageNegotiatorInterface.php
index d12fd6f..73bef59 100644
--- a/core/modules/language/lib/Drupal/language/LanguageNegotiatorInterface.php
+++ b/core/modules/language/lib/Drupal/language/LanguageNegotiatorInterface.php
@@ -41,7 +41,7 @@
  * configurable:
  * @code
  * function mymodule_language_types_info_alter(&$language_types) {
- *   unset($language_types[Language::TYPE_CONTENT]['fixed']);
+ *   unset($language_types[LanguageInterface::TYPE_CONTENT]['fixed']);
  * }
  * @endcode
  *
@@ -91,7 +91,7 @@
  *       // If we are on an administrative path, override with the default
  *       language.
  *       if ($request->query->has('q') && strtok($request->query->get('q'), '/') == 'admin') {
- *         return $this->languageManager->getDefaultLanguage()->id;
+ *         return $this->languageManager->getDefaultLanguage()->getId();
  *       }
  *       return $langcode;
  *     }
diff --git a/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php b/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php
index 95eb700..4f81af8 100644
--- a/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php
+++ b/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Config\BootstrapConfigStorageFactory;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\DependencyInjection\ServiceProviderBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface as CoreLanguageInterface;
 use Symfony\Component\DependencyInjection\Reference;
 
 /**
@@ -81,7 +81,7 @@ protected function isMultilingual() {
     //   container has finished building.
     $config_storage = BootstrapConfigStorageFactory::get();
     $config_ids = array_filter($config_storage->listAll($prefix), function($config_id) use ($prefix) {
-      return $config_id != $prefix . Language::LANGCODE_NOT_SPECIFIED && $config_id != $prefix . Language::LANGCODE_NOT_APPLICABLE;
+      return $config_id != $prefix . CoreLanguageInterface::LANGCODE_NOT_SPECIFIED && $config_id != $prefix . CoreLanguageInterface::LANGCODE_NOT_APPLICABLE;
     });
     return count($config_ids) > 1;
   }
diff --git a/core/modules/language/lib/Drupal/language/Plugin/Condition/Language.php b/core/modules/language/lib/Drupal/language/Plugin/Condition/Language.php
index 9dda571..cc20f42 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/Condition/Language.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/Condition/Language.php
@@ -72,8 +72,8 @@ public function summary() {
     $language_names = array_reduce($language_list, function(&$result, $item) use ($selected) {
       // If the current item of the $language_list array is one of the selected
       // languages, add it to the $results array.
-      if (!empty($selected[$item->id])) {
-        $result[$item->id] = $item->name;
+      if (!empty($selected[$item->getId()])) {
+        $result[$item->getId()] = $item->getName();
       }
       return $result;
     }, array());
@@ -99,7 +99,7 @@ public function evaluate() {
     $language = $this->getContextValue('language');
     // Language visibility settings.
     if (!empty($this->configuration['langcodes'])) {
-      return !empty($this->configuration['langcodes'][$language->id]);
+      return !empty($this->configuration['langcodes'][$language->getId()]);
     }
     return TRUE;
   }
diff --git a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationSession.php b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationSession.php
index e56278d..d20a187 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationSession.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationSession.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\language\Plugin\LanguageNegotiation;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\PathProcessor\OutboundPathProcessorInterface;
 use Drupal\language\LanguageNegotiationMethodBase;
 use Drupal\language\LanguageSwitcherInterface;
@@ -68,12 +68,12 @@ public function getLangcode(Request $request = NULL) {
   /**
    * {@inheritdoc}
    */
-  public function persist(Language $language) {
+  public function persist(LanguageInterface $language) {
     parent::persist($language);
 
     // We need to update the session parameter with the request value only if we
     // have an authenticated user.
-    $langcode = $language->id;
+    $langcode = $language->getId();
     if ($langcode && $this->languageManager) {
       $languages = $this->languageManager->getLanguages();
       if ($this->currentUser->isAuthenticated() && isset($languages[$langcode])) {
@@ -127,15 +127,15 @@ function getLanguageSwitchLinks(Request $request, $type, $path) {
     $links = array();
     $config = $this->config->get('language.negotiation')->get('session');
     $param = $config['parameter'];
-    $language_query = isset($_SESSION[$param]) ? $_SESSION[$param] : $this->languageManager->getCurrentLanguage($type)->id;
+    $language_query = isset($_SESSION[$param]) ? $_SESSION[$param] : $this->languageManager->getCurrentLanguage($type)->getId();
     $query = array();
     parse_str($request->getQueryString(), $query);
 
     foreach ($this->languageManager->getLanguages() as $language) {
-      $langcode = $language->id;
+      $langcode = $language->getId();
       $links[$langcode] = array(
         'href' => $path,
-        'title' => $language->name,
+        'title' => $language->getName(),
         'attributes' => array('class' => array('language-link')),
         'query' => $query,
       );
diff --git a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUI.php b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUI.php
index 3b64974..fd7eb75 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUI.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUI.php
@@ -15,7 +15,7 @@
  *
  * @Plugin(
  *   id = Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUI::METHOD_ID,
- *   types = {Drupal\Core\Language\Language::TYPE_CONTENT},
+ *   types = {Drupal\Core\Language\LanguageInterface::TYPE_CONTENT},
  *   weight = 9,
  *   name = @Translation("Interface"),
  *   description = @Translation("Use the detected interface language.")
@@ -32,7 +32,7 @@ class LanguageNegotiationUI extends LanguageNegotiationMethodBase {
    * {@inheritdoc}
    */
   public function getLangcode(Request $request = NULL) {
-    return $this->languageManager ? $this->languageManager->getCurrentLanguage()->id : NULL;
+    return $this->languageManager ? $this->languageManager->getCurrentLanguage()->getId() : NULL;
   }
 
 }
diff --git a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php
index 42a0933..d869d4f 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\language\Plugin\LanguageNegotiation;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\PathProcessor\InboundPathProcessorInterface;
 use Drupal\Core\PathProcessor\OutboundPathProcessorInterface;
 use Drupal\language\LanguageNegotiationMethodBase;
@@ -19,7 +19,7 @@
  *
  * @Plugin(
  *   id = \Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl::METHOD_ID,
- *   types = {\Drupal\Core\Language\Language::TYPE_INTERFACE, \Drupal\Core\Language\Language::TYPE_CONTENT, \Drupal\Core\Language\Language::TYPE_URL},
+ *   types = {\Drupal\Core\Language\LanguageInterface::TYPE_INTERFACE, \Drupal\Core\Language\LanguageInterface::TYPE_CONTENT, \Drupal\Core\Language\LanguageInterface::TYPE_URL},
  *   weight = -8,
  *   name = @Translation("URL"),
  *   description = @Translation("Language from the URL (Path prefix or domain)."),
@@ -62,14 +62,14 @@ public function getLangcode(Request $request = NULL) {
           // Search prefix within added languages.
           $negotiated_language = FALSE;
           foreach ($languages as $language) {
-            if (isset($config['prefixes'][$language->id]) && $config['prefixes'][$language->id] == $prefix) {
+            if (isset($config['prefixes'][$language->getId()]) && $config['prefixes'][$language->getId()] == $prefix) {
               $negotiated_language = $language;
               break;
             }
           }
 
           if ($negotiated_language) {
-            $langcode = $negotiated_language->id;
+            $langcode = $negotiated_language->getId();
           }
           break;
 
@@ -78,13 +78,13 @@ public function getLangcode(Request $request = NULL) {
           $http_host = $request->getHost();
           foreach ($languages as $language) {
             // Skip the check if the language doesn't have a domain.
-            if (!empty($config['domains'][$language->id])) {
+            if (!empty($config['domains'][$language->getId()])) {
               // Ensure that there is exactly one protocol in the URL when
               // checking the hostname.
-              $host = 'http://' . str_replace(array('http://', 'https://'), '', $config['domains'][$language->id]);
+              $host = 'http://' . str_replace(array('http://', 'https://'), '', $config['domains'][$language->getId()]);
               $host = parse_url($host, PHP_URL_HOST);
               if ($http_host == $host) {
-                $langcode = $language->id;
+                $langcode = $language->getId();
                 break;
               }
             }
@@ -106,7 +106,7 @@ public function processInbound($path, Request $request) {
 
     // Search prefix within added languages.
     foreach ($this->languageManager->getLanguages() as $language) {
-      if (isset($config['prefixes'][$language->id]) && $config['prefixes'][$language->id] == $prefix) {
+      if (isset($config['prefixes'][$language->getId()]) && $config['prefixes'][$language->getId()] == $prefix) {
         // Rebuild $path with the language removed.
         $path = implode('/', $parts);
         break;
@@ -129,21 +129,21 @@ public function processOutbound($path, &$options = array(), Request $request = N
     $languages = array_flip(array_keys($this->languageManager->getLanguages()));
     // Language can be passed as an option, or we go for current URL language.
     if (!isset($options['language'])) {
-      $language_url = $this->languageManager->getCurrentLanguage(Language::TYPE_URL);
+      $language_url = $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_URL);
       $options['language'] = $language_url;
     }
     // We allow only added languages here.
-    elseif (!is_object($options['language']) || !isset($languages[$options['language']->id])) {
+    elseif (!is_object($options['language']) || !isset($languages[$options['language']->getId()])) {
       return $path;
     }
     $config = $this->config->get('language.negotiation')->get('url');
     if ($config['source'] == LanguageNegotiationUrl::CONFIG_PATH_PREFIX) {
-      if (is_object($options['language']) && !empty($config['prefixes'][$options['language']->id])) {
-        return empty($path) ? $config['prefixes'][$options['language']->id] : $config['prefixes'][$options['language']->id] . '/' . $path;
+      if (is_object($options['language']) && !empty($config['prefixes'][$options['language']->getId()])) {
+        return empty($path) ? $config['prefixes'][$options['language']->getId()] : $config['prefixes'][$options['language']->getId()] . '/' . $path;
       }
     }
     elseif ($config['source'] ==  LanguageNegotiationUrl::CONFIG_DOMAIN) {
-      if (is_object($options['language']) && !empty($config['domains'][$options['language']->id])) {
+      if (is_object($options['language']) && !empty($config['domains'][$options['language']->getId()])) {
 
         // Save the original base URL. If it contains a port, we need to
         // retain it below.
@@ -154,7 +154,7 @@ public function processOutbound($path, &$options = array(), Request $request = N
 
         // Ask for an absolute URL with our modified base URL.
         $options['absolute'] = TRUE;
-        $options['base_url'] = $url_scheme . '://' . $config['domains'][$options['language']->id];
+        $options['base_url'] = $url_scheme . '://' . $config['domains'][$options['language']->getId()];
 
         // In case either the original base URL or the HTTP host contains a
         // port, retain it.
@@ -189,9 +189,9 @@ function getLanguageSwitchLinks(Request $request, $type, $path) {
     $links = array();
 
     foreach ($this->languageManager->getLanguages() as $language) {
-      $links[$language->id] = array(
+      $links[$language->getId()] = array(
         'href' => $path,
-        'title' => $language->name,
+        'title' => $language->getName(),
         'language' => $language,
         'attributes' => array('class' => array('language-link')),
       );
diff --git a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrlFallback.php b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrlFallback.php
index 2310153..abaa6e3 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrlFallback.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationUrlFallback.php
@@ -34,7 +34,7 @@
  *
  * @Plugin(
  *   id = Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrlFallback::METHOD_ID,
- *   types = {Drupal\Core\Language\Language::TYPE_URL},
+ *   types = {Drupal\Core\Language\LanguageInterface::TYPE_URL},
  *   weight = 8,
  *   name = @Translation("URL fallback"),
  *   description = @Translation("Use an already detected language for URLs if none is found.")
@@ -62,11 +62,11 @@ public function getLangcode(Request $request = NULL) {
       // information, a missing URL language information indicates that URL
       // language should be the default one, otherwise we fall back to an
       // already detected language.
-      if (($prefix && empty($config['prefixes'][$default->id])) || (!$prefix && empty($config['domains'][$default->id]))) {
-        $langcode = $default->id;
+      if (($prefix && empty($config['prefixes'][$default->getId()])) || (!$prefix && empty($config['domains'][$default->getId()]))) {
+        $langcode = $default->getId();
       }
       else {
-        $langcode = $this->languageManager->getCurrentLanguage()->id;
+        $langcode = $this->languageManager->getCurrentLanguage()->getId();
       }
     }
 
diff --git a/core/modules/language/lib/Drupal/language/Plugin/views/field/LanguageField.php b/core/modules/language/lib/Drupal/language/Plugin/views/field/LanguageField.php
index 3909fcd..152104d 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/views/field/LanguageField.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/views/field/LanguageField.php
@@ -44,7 +44,7 @@ public function render(ResultRow $values) {
     // ready, see http://drupal.org/node/1616594.
     $value = $this->getValue($values);
     $language = language_load($value);
-    return $language ? $language->name : '';
+    return $language ? $language->getName() : '';
   }
 
 }
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationElementTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationElementTest.php
index c7c85f1..f9721a7 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationElementTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationElementTest.php
@@ -84,17 +84,17 @@ public function testDefaultLangcode() {
     language_save_default_configuration('custom_type', 'custom_bundle', array('langcode' => 'current_interface', 'language_show' => TRUE));
     $langcode = language_get_default_langcode('custom_type', 'custom_bundle');
     $language_interface = \Drupal::languageManager()->getCurrentLanguage();
-    $this->assertEqual($langcode, $language_interface->id);
+    $this->assertEqual($langcode, $language_interface->getId());
 
     // Site's default.
     $old_default = \Drupal::languageManager()->getDefaultLanguage();
     // Ensure the language entity default value is correct.
     $language_entity = entity_load('language_entity', $old_default->getId());
     $this->assertTrue($language_entity->get('default'), 'The en language entity is flagged as the default language.');
-    $old_default->default = FALSE;
+    $old_default->setDefault(FALSE);
     language_save($old_default);
     $new_default = \Drupal::languageManager()->getLanguage('cc');
-    $new_default->default = TRUE;
+    $new_default->setDefault(TRUE);
     language_save($new_default);
     language_save_default_configuration('custom_type', 'custom_bundle', array('langcode' => 'site_default', 'language_show' => TRUE));
     $langcode = language_get_default_langcode('custom_type', 'custom_bundle');
@@ -104,7 +104,7 @@ public function testDefaultLangcode() {
     $language_entity = entity_load('language_entity', $old_default->getId());
     $this->assertFalse($language_entity->get('default'), 'The en language entity is not flagged as the default language.');
     $language_entity = entity_load('language_entity', 'cc');
-    // Check calling the Drupal\language\Entity\Language::isDefault() method
+    // Check calling the Drupal\language\Entity\LanguageInterface::isDefault() method
     // directly.
     $this->assertTrue($language_entity->isDefault(), 'The cc language entity is flagged as the default language.');
 
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationTest.php
index 6093263..03edfaf 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\language\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -160,9 +160,9 @@ protected function checkConfigurableLanguageWeight($state = 'by default') {
     \Drupal::languageManager()->reset();
     $max_configurable_language_weight = $this->getHighestConfigurableLanguageWeight();
     $replacements = array('@event' => $state);
-    foreach (\Drupal::languageManager()->getLanguages(Language::STATE_LOCKED) as $locked_language) {
-      $replacements['%language'] = $locked_language->name;
-      $this->assertTrue($locked_language->weight > $max_configurable_language_weight, format_string('System language %language has higher weight than configurable languages @event', $replacements));
+    foreach (\Drupal::languageManager()->getLanguages(LanguageInterface::STATE_LOCKED) as $locked_language) {
+      $replacements['%language'] = $locked_language->getName();
+      $this->assertTrue($locked_language->getWeight() > $max_configurable_language_weight, format_string('System language %language has higher weight than configurable languages @event', $replacements));
     }
   }
 
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php
index 9554dd8..5a34b85 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\language\Tests;
 
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
 
@@ -49,7 +50,7 @@ public function testLanguageConfiguration() {
     $this->assertText(t('!name field is required.', array('!name' => t('Language code'))));
     $this->assertText(t('!name field is required.', array('!name' => t('Language name in English'))));
     $empty_language = new Language();
-    $this->assertFieldChecked('edit-direction-' . $empty_language->direction, 'Consistent usage of language direction.');
+    $this->assertFieldChecked('edit-direction-' . $empty_language->getDirection(), 'Consistent usage of language direction.');
     $this->assertEqual($this->getUrl(), url('admin/config/regional/language/add', array('absolute' => TRUE)), 'Correct page redirection.');
 
     // Test validation of invalid values.
@@ -57,7 +58,7 @@ public function testLanguageConfiguration() {
       'predefined_langcode' => 'custom',
       'langcode' => 'white space',
       'name' => '<strong>evil markup</strong>',
-      'direction' => Language::DIRECTION_LTR,
+      'direction' => LanguageInterface::DIRECTION_LTR,
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
     $this->assertRaw(t('%field may only contain characters a-z, underscores, or hyphens.', array('%field' => t('Language code'))));
@@ -69,7 +70,7 @@ public function testLanguageConfiguration() {
       'predefined_langcode' => 'custom',
       'langcode' => 'de',
       'name' => 'German',
-      'direction' => Language::DIRECTION_LTR,
+      'direction' => LanguageInterface::DIRECTION_LTR,
     );
 
     // Add the language the first time.
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageDependencyInjectionTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageDependencyInjectionTest.php
index 067c477..7701e13 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageDependencyInjectionTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageDependencyInjectionTest.php
@@ -62,7 +62,7 @@ function testDependencyInjectedNewDefaultLanguage() {
     // The language system creates a Language object which contains the
     // same properties as the new default language object.
     $result = \Drupal::languageManager()->getCurrentLanguage();
-    $this->assertIdentical($result->id, 'fr');
+    $this->assertIdentical($result->getId(), 'fr');
 
     // Delete the language to check that we fallback to the default.
     try {
@@ -77,7 +77,7 @@ function testDependencyInjectedNewDefaultLanguage() {
     language_save($default_language);
     language_delete('fr');
     $result = \Drupal::languageManager()->getCurrentLanguage();
-    $this->assertIdentical($result->id, $default_language->id);
+    $this->assertIdentical($result->getId(), $default_language->getId());
   }
 
 }
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageFallbackTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageFallbackTest.php
index fb621d8..b35fce9 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageFallbackTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageFallbackTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\language\Tests;
 
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests the language fallback behavior.
@@ -30,8 +31,8 @@ protected function setUp() {
 
     for ($i = 0; $i < 3; $i++) {
       $language = new Language();
-      $language->id = $this->randomName(2);
-      $language->weight = -$i;
+      $language->setId($this->randomName(2));
+      $language->setWeight(-$i);
       language_save($language);
     }
   }
@@ -41,7 +42,7 @@ protected function setUp() {
    */
   public function testCandidates() {
     $language_list = $this->languageManager->getLanguages();
-    $expected = array_keys($language_list + array(Language::LANGCODE_NOT_SPECIFIED => NULL));
+    $expected = array_keys($language_list + array(LanguageInterface::LANGCODE_NOT_SPECIFIED => NULL));
 
     // Check that language fallback candidates by default are all the available
     // languages sorted by weight.
@@ -57,20 +58,20 @@ public function testCandidates() {
     // Check that candidates are alterable for specific operations.
     $this->state->set('language_test.fallback_alter.candidates', FALSE);
     $this->state->set('language_test.fallback_operation_alter.candidates', TRUE);
-    $expected[] = Language::LANGCODE_NOT_SPECIFIED;
-    $expected[] = Language::LANGCODE_NOT_APPLICABLE;
+    $expected[] = LanguageInterface::LANGCODE_NOT_SPECIFIED;
+    $expected[] = LanguageInterface::LANGCODE_NOT_APPLICABLE;
     $candidates = $this->languageManager->getFallbackCandidates(NULL, array('operation' => 'test'));
     $this->assertEqual(array_values($candidates), $expected, 'Language fallback candidates are alterable for specific operations.');
 
     // Check that when the site is monolingual no language fallback is applied.
-    $default_langcode = $this->languageManager->getDefaultLanguage()->id;
+    $default_langcode = $this->languageManager->getDefaultLanguage()->getId();
     foreach ($language_list as $langcode => $language) {
       if ($langcode != $default_langcode) {
         language_delete($langcode);
       }
     }
     $candidates = $this->languageManager->getFallbackCandidates();
-    $this->assertEqual(array_values($candidates), array(Language::LANGCODE_DEFAULT), 'Language fallback is not applied when the Language module is not enabled.');
+    $this->assertEqual(array_values($candidates), array(LanguageInterface::LANGCODE_DEFAULT), 'Language fallback is not applied when the Language module is not enabled.');
   }
 
 }
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
index d5abded..2482bf9 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\language\Tests;
 
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
 
@@ -179,10 +180,10 @@ function testLanguageStates() {
     $expected_all_languages = array('l4' => 'l4', 'l3' => 'l3', 'l2' => 'l2', 'l1' => 'l1', 'en' => 'en', 'und' => 'und', 'zxx' => 'zxx');
     $expected_conf_languages = array('l3' => 'l3', 'l1' => 'l1', 'en' => 'en');
 
-    $locked_languages = $this->container->get('language_manager')->getLanguages(Language::STATE_LOCKED);
+    $locked_languages = $this->container->get('language_manager')->getLanguages(LanguageInterface::STATE_LOCKED);
     $this->assertEqual(array_diff_key($expected_locked_languages, $locked_languages), array(), 'Locked languages loaded correctly.');
 
-    $all_languages = $this->container->get('language_manager')->getLanguages(Language::STATE_ALL);
+    $all_languages = $this->container->get('language_manager')->getLanguages(LanguageInterface::STATE_ALL);
     $this->assertEqual(array_diff_key($expected_all_languages, $all_languages), array(), 'All languages loaded correctly.');
 
     $conf_languages = $this->container->get('language_manager')->getLanguages();
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageNegotiationInfoTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageNegotiationInfoTest.php
index 70d297c..a3245ca 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageNegotiationInfoTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageNegotiationInfoTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\language\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUI;
 use Drupal\simpletest\WebTestBase;
 
@@ -81,7 +81,7 @@ function testInfoAlterations() {
       'language_test.language_types' => TRUE,
       // Enable language_test negotiation info (not altered yet).
       'language_test.language_negotiation_info' => TRUE,
-      // Alter Language::TYPE_CONTENT to be configurable.
+      // Alter LanguageInterface::TYPE_CONTENT to be configurable.
       'language_test.content_language_type' => TRUE,
     ));
     $this->container->get('module_handler')->install(array('language_test'));
@@ -91,7 +91,7 @@ function testInfoAlterations() {
     // of saving the language negotiation settings.
     $this->checkFixedLanguageTypes();
 
-    $type = Language::TYPE_CONTENT;
+    $type = LanguageInterface::TYPE_CONTENT;
     $language_types = $this->languageManager()->getLanguageTypes();
     $this->assertTrue(in_array($type, $language_types), 'Content language type is configurable.');
 
@@ -138,7 +138,7 @@ function testInfoAlterations() {
     $last = $this->container->get('state')->get('language_test.language_negotiation_last');
     foreach ($this->languageManager()->getDefinedLanguageTypes() as $type) {
       $langcode = $last[$type];
-      $value = $type == Language::TYPE_CONTENT || strpos($type, 'test') !== FALSE ? 'it' : 'en';
+      $value = $type == LanguageInterface::TYPE_CONTENT || strpos($type, 'test') !== FALSE ? 'it' : 'en';
       $this->assertEqual($langcode, $value, format_string('The negotiated language for %type is %language', array('%type' => $type, '%language' => $value)));
     }
 
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguagePathMonolingualTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguagePathMonolingualTest.php
index 73e5b85..7548b90 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguagePathMonolingualTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguagePathMonolingualTest.php
@@ -57,7 +57,7 @@ function setUp() {
     // Verify that French is the only language.
     $this->container->get('language_manager')->reset();
     $this->assertFalse(\Drupal::languageManager()->isMultilingual(), 'Site is mono-lingual');
-    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->id, 'fr', 'French is the default language');
+    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->getId(), 'fr', 'French is the default language');
 
     // Set language detection to URL.
     $edit = array('language_interface[enabled][language-url]' => TRUE);
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageSwitchingTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageSwitchingTest.php
index b4c4616..d7609cc 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageSwitchingTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageSwitchingTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\language\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -43,7 +43,7 @@ function setUp() {
    */
   function testLanguageBlock() {
     // Enable the language switching block..
-    $block = $this->drupalPlaceBlock('language_block:' . Language::TYPE_INTERFACE, array(
+    $block = $this->drupalPlaceBlock('language_block:' . LanguageInterface::TYPE_INTERFACE, array(
       'id' => 'test_language_block',
       // Ensure a 2-byte UTF-8 sequence is in the tested output.
       'label' => $this->randomName(8) . '×',
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
index 1a2e5d6..743910b 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\language\Tests;
 
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationBrowser;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationSelected;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
@@ -243,7 +244,7 @@ function testUILanguageNegotiation() {
     // Unknown language prefix should return 404.
     $definitions = \Drupal::languageManager()->getNegotiator()->getNegotiationMethods();
     \Drupal::config('language.types')
-      ->set('negotiation.' . Language::TYPE_INTERFACE . '.enabled', array_flip(array_keys($definitions)))
+      ->set('negotiation.' . LanguageInterface::TYPE_INTERFACE . '.enabled', array_flip(array_keys($definitions)))
       ->save();
     $this->drupalGet("$langcode_unknown/admin/config", array(), $http_header_browser_fallback);
     $this->assertResponse(404, "Unknown language path prefix should return 404");
@@ -338,7 +339,7 @@ function testUILanguageNegotiation() {
   protected function runTest($test) {
     if (!empty($test['language_negotiation'])) {
       $method_weights = array_flip($test['language_negotiation']);
-      $this->container->get('language_negotiator')->saveConfiguration(Language::TYPE_INTERFACE, $method_weights);
+      $this->container->get('language_negotiator')->saveConfiguration(LanguageInterface::TYPE_INTERFACE, $method_weights);
     }
     if (!empty($test['language_negotiation_url_part'])) {
       \Drupal::config('language.negotiation')
@@ -382,7 +383,7 @@ function testUrlLanguageFallback() {
     $this->drupalGet('admin/config/regional/language/detection');
 
     // Enable the language switcher block.
-    $this->drupalPlaceBlock('language_block:' . Language::TYPE_INTERFACE, array('id' => 'test_language_block'));
+    $this->drupalPlaceBlock('language_block:' . LanguageInterface::TYPE_INTERFACE, array('id' => 'test_language_block'));
 
     // Log out, because for anonymous users, the "active" class is set by PHP
     // (which means we can easily test it here), whereas for authenticated users
@@ -399,7 +400,7 @@ function testUrlLanguageFallback() {
     // language.
     $args = array(':id' => 'block-test-language-block', ':url' => base_path() . $GLOBALS['script_path'] . $langcode_browser_fallback);
     $fields = $this->xpath('//div[@id=:id]//a[@class="language-link active" and starts-with(@href, :url)]', $args);
-    $this->assertTrue($fields[0] == $languages[$langcode_browser_fallback]->name, 'The browser language is the URL active language');
+    $this->assertTrue($fields[0] == $languages[$langcode_browser_fallback]->getName(), 'The browser language is the URL active language');
 
     // Check that URLs are rewritten using the given browser language.
     $fields = $this->xpath('//strong[@class="site-name"]/a[@rel="home" and @href=:url]', $args);
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageUrlRewritingTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageUrlRewritingTest.php
index 39ad3f8..852d75c 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageUrlRewritingTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageUrlRewritingTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\language\Tests;
 
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
 use Drupal\simpletest\WebTestBase;
 use Symfony\Component\HttpFoundation\Request;
@@ -55,7 +56,7 @@ function setUp() {
   function testUrlRewritingEdgeCases() {
     // Check URL rewriting with a non-installed language.
     $non_existing = \Drupal::languageManager()->getDefaultLanguage();
-    $non_existing->id = $this->randomName();
+    $non_existing->setId($this->randomName());
     $this->checkUrl($non_existing, 'Path language is ignored if language is not installed.', 'URL language negotiation does not work with non-installed languages');
 
     $request = $this->prepareRequestForGenerator();
@@ -71,14 +72,13 @@ function testUrlRewritingEdgeCases() {
    * check that language prefixes are not added to it and that the prefixed URL
    * is actually not working.
    *
-   * @param string $language
-   *   The language prefix, e.g. 'es'.
+   * @param \Drupal\Core\Language\LanguageInterface $language
    * @param string $message1
    *   Message to display in assertion that language prefixes are not added.
    * @param string $message2
    *   The message to display confirming prefixed URL is not working.
    */
-  private function checkUrl($language, $message1, $message2) {
+  private function checkUrl(LanguageInterface $language, $message1, $message2) {
     $options = array('language' => $language, 'script' => '');
     $base_path = trim(base_path(), '/');
     $rewritten_path = trim(str_replace($base_path, '', url('node', $options)), '/');
@@ -89,7 +89,7 @@ private function checkUrl($language, $message1, $message2) {
     // If the rewritten URL has not a language prefix we pick a random prefix so
     // we can always check the prefixed URL.
     $prefixes = language_negotiation_url_prefixes();
-    $stored_prefix = isset($prefixes[$language->id]) ? $prefixes[$language->id] : $this->randomName();
+    $stored_prefix = isset($prefixes[$language->getId()]) ? $prefixes[$language->getId()] : $this->randomName();
     if ($this->assertNotEqual($stored_prefix, $prefix, $message1)) {
       $prefix = $stored_prefix;
     }
diff --git a/core/modules/language/lib/Drupal/language/Tests/Views/ArgumentLanguageTest.php b/core/modules/language/lib/Drupal/language/Tests/Views/ArgumentLanguageTest.php
index f25b251..83111d7 100644
--- a/core/modules/language/lib/Drupal/language/Tests/Views/ArgumentLanguageTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/Views/ArgumentLanguageTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\language\Tests\Views;
 
-use Drupal\Core\Language\Language;
 use Drupal\views\Views;
 
 /**
diff --git a/core/modules/language/lib/Drupal/language/Tests/Views/FieldLanguageTest.php b/core/modules/language/lib/Drupal/language/Tests/Views/FieldLanguageTest.php
index 13b5135..bc082e3 100644
--- a/core/modules/language/lib/Drupal/language/Tests/Views/FieldLanguageTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/Views/FieldLanguageTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\language\Tests\Views;
 
-use Drupal\Core\Language\Language;
 use Drupal\views\Views;
 
 /**
diff --git a/core/modules/language/lib/Drupal/language/Tests/Views/FilterLanguageTest.php b/core/modules/language/lib/Drupal/language/Tests/Views/FilterLanguageTest.php
index 87717f6..f3db7c5 100644
--- a/core/modules/language/lib/Drupal/language/Tests/Views/FilterLanguageTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/Views/FilterLanguageTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\language\Tests\Views;
 
-use Drupal\Core\Language\Language;
 use Drupal\views\Views;
 
 /**
diff --git a/core/modules/language/tests/Drupal/language/Tests/LanguageNegotiationUrlTest.php b/core/modules/language/tests/Drupal/language/Tests/LanguageNegotiationUrlTest.php
index 6a4df28..1926cd5 100644
--- a/core/modules/language/tests/Drupal/language/Tests/LanguageNegotiationUrlTest.php
+++ b/core/modules/language/tests/Drupal/language/Tests/LanguageNegotiationUrlTest.php
@@ -38,13 +38,17 @@ public static function getInfo() {
   public function setUp() {
 
     // Set up some languages to be used by the language-based path processor.
+    $language_de = $this->getMock('\Drupal\Core\Language\LanguageInterface');
+    $language_de->expects($this->any())
+      ->method('getId')
+      ->will($this->returnValue('de'));
+    $language_en = $this->getMock('\Drupal\Core\Language\LanguageInterface');
+    $language_en->expects($this->any())
+      ->method('getId')
+      ->will($this->returnValue('en'));
     $languages = array(
-      'de' => (object) array(
-        'id' => 'de',
-      ),
-      'en' => (object) array(
-        'id' => 'en',
-      ),
+      'de' => $language_de,
+      'en' => $language_en,
     );
 
     // Create a language manager stub.
diff --git a/core/modules/language/tests/language_test/language_test.module b/core/modules/language/tests/language_test/language_test.module
index e1fd47e..fa34a33 100644
--- a/core/modules/language/tests/language_test/language_test.module
+++ b/core/modules/language/tests/language_test/language_test.module
@@ -5,7 +5,7 @@
  * Mock module for language layer tests.
  */
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUI;
 
 /**
@@ -13,8 +13,8 @@
  */
 function language_test_page_build() {
   language_test_store_language_negotiation();
-  if (isset(\Drupal::languageManager()->getCurrentLanguage()->id) && isset(\Drupal::languageManager()->getCurrentLanguage()->method_id)) {
-    drupal_set_message(t('Language negotiation method: @name', array('@name' => \Drupal::languageManager()->getCurrentLanguage()->method_id)));
+  if (\Drupal::languageManager()->getCurrentLanguage()->getId() && \Drupal::languageManager()->getCurrentLanguage()->getNegotiationMethodId()) {
+    drupal_set_message(t('Language negotiation method: @name', array('@name' => \Drupal::languageManager()->getCurrentLanguage()->getNegotiationMethodId())));
   }
 }
 
@@ -41,13 +41,13 @@ function language_test_language_types_info() {
  */
 function language_test_language_types_info_alter(array &$language_types) {
   if (\Drupal::state()->get('language_test.content_language_type')) {
-    $language_types[Language::TYPE_CONTENT]['locked'] = FALSE;
-    unset($language_types[Language::TYPE_CONTENT]['fixed']);
-    // By default languages are not configurable. Make Language::TYPE_CONTENT
+    $language_types[LanguageInterface::TYPE_CONTENT]['locked'] = FALSE;
+    unset($language_types[LanguageInterface::TYPE_CONTENT]['fixed']);
+    // By default languages are not configurable. Make LanguageInterface::TYPE_CONTENT
     // configurable.
     $configurable = \Drupal::config('language.types')->get('configurable');
-    if (!in_array(Language::TYPE_CONTENT, $configurable)) {
-      $configurable[] = Language::TYPE_CONTENT;
+    if (!in_array(LanguageInterface::TYPE_CONTENT, $configurable)) {
+      $configurable[] = LanguageInterface::TYPE_CONTENT;
       \Drupal::config('language.types')->set('configurable', $configurable)->save();
     }
   }
@@ -69,7 +69,7 @@ function language_test_store_language_negotiation() {
   if (\Drupal::moduleHandler()->moduleExists('language')) {
     $last = array();
     foreach (\Drupal::languageManager()->getDefinedLanguageTypes() as $type) {
-      $last[$type] = \Drupal::languageManager()->getCurrentLanguage($type)->id;
+      $last[$type] = \Drupal::languageManager()->getCurrentLanguage($type)->getId();
     }
     \Drupal::state()->set('language_test.language_negotiation_last', $last);
   }
@@ -80,7 +80,7 @@ function language_test_store_language_negotiation() {
  */
 function language_test_language_fallback_candidates_alter(array &$candidates, array $context) {
   if (Drupal::state()->get('language_test.fallback_alter.candidates')) {
-    unset($candidates[Language::LANGCODE_NOT_SPECIFIED]);
+    unset($candidates[LanguageInterface::LANGCODE_NOT_SPECIFIED]);
   }
 }
 
@@ -89,7 +89,7 @@ function language_test_language_fallback_candidates_alter(array &$candidates, ar
  */
 function language_test_language_fallback_candidates_test_alter(array &$candidates, array $context) {
   if (Drupal::state()->get('language_test.fallback_operation_alter.candidates')) {
-    $langcode = Language::LANGCODE_NOT_APPLICABLE;
+    $langcode = LanguageInterface::LANGCODE_NOT_APPLICABLE;
     $candidates[$langcode] = $langcode;
   }
 }
diff --git a/core/modules/language/tests/language_test/lib/Drupal/language_test/Plugin/LanguageNegotiation/LanguageNegotiationTest.php b/core/modules/language/tests/language_test/lib/Drupal/language_test/Plugin/LanguageNegotiation/LanguageNegotiationTest.php
index a726c5c..61b02c1 100644
--- a/core/modules/language/tests/language_test/lib/Drupal/language_test/Plugin/LanguageNegotiation/LanguageNegotiationTest.php
+++ b/core/modules/language/tests/language_test/lib/Drupal/language_test/Plugin/LanguageNegotiation/LanguageNegotiationTest.php
@@ -18,7 +18,7 @@
  *   weight = -10,
  *   name = @Translation("Test"),
  *   description = @Translation("This is a test language negotiation method."),
- *   types = {Drupal\Core\Language\Language::TYPE_CONTENT, "test_language_type", "fixed_test_language_type"}
+ *   types = {Drupal\Core\Language\LanguageInterface::TYPE_CONTENT, "test_language_type", "fixed_test_language_type"}
  * )
  */
 class LanguageNegotiationTest extends LanguageNegotiationMethodBase {
diff --git a/core/modules/locale/lib/Drupal/locale/Form/ExportForm.php b/core/modules/locale/lib/Drupal/locale/Form/ExportForm.php
index 433c8c9..89adf49 100644
--- a/core/modules/locale/lib/Drupal/locale/Form/ExportForm.php
+++ b/core/modules/locale/lib/Drupal/locale/Form/ExportForm.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Gettext\PoStreamWriter;
 use Drupal\Core\Form\FormBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\locale\PoDatabaseReader;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -61,7 +61,7 @@ public function buildForm(array $form, array &$form_state) {
     $language_options = array();
     foreach ($languages as $langcode => $language) {
       if ($langcode != 'en' || locale_translate_english()) {
-        $language_options[$langcode] = $language->name;
+        $language_options[$langcode] = $language->getName();
       }
     }
     $language_default = $this->languageManager->getDefaultLanguage();
@@ -69,7 +69,7 @@ public function buildForm(array $form, array &$form_state) {
     if (empty($language_options)) {
       $form['langcode'] = array(
         '#type' => 'value',
-        '#value' => Language::LANGCODE_SYSTEM,
+        '#value' => LanguageInterface::LANGCODE_SYSTEM,
       );
       $form['langcode_text'] = array(
         '#type' => 'item',
@@ -82,9 +82,9 @@ public function buildForm(array $form, array &$form_state) {
         '#type' => 'select',
         '#title' => $this->t('Language'),
         '#options' => $language_options,
-        '#default_value' => $language_default->id,
+        '#default_value' => $language_default->getId(),
         '#empty_option' => $this->t('Source text only, no translations'),
-        '#empty_value' => Language::LANGCODE_SYSTEM,
+        '#empty_value' => LanguageInterface::LANGCODE_SYSTEM,
       );
       $form['content_options'] = array(
         '#type' => 'details',
@@ -93,7 +93,7 @@ public function buildForm(array $form, array &$form_state) {
         '#tree' => TRUE,
         '#states' => array(
           'invisible' => array(
-            ':input[name="langcode"]' => array('value' => Language::LANGCODE_SYSTEM),
+            ':input[name="langcode"]' => array('value' => LanguageInterface::LANGCODE_SYSTEM),
           ),
         ),
       );
@@ -129,7 +129,7 @@ public function buildForm(array $form, array &$form_state) {
    */
   public function submitForm(array &$form, array &$form_state) {
     // If template is required, language code is not given.
-    if ($form_state['values']['langcode'] != Language::LANGCODE_SYSTEM) {
+    if ($form_state['values']['langcode'] != LanguageInterface::LANGCODE_SYSTEM) {
       $language = $this->languageManager->getLanguage($form_state['values']['langcode']);
     }
     else {
@@ -139,11 +139,11 @@ public function submitForm(array &$form, array &$form_state) {
     $reader = new PoDatabaseReader();
     $languageName = '';
     if ($language != NULL) {
-      $reader->setLangcode($language->id);
+      $reader->setLangcode($language->getId());
       $reader->setOptions($content_options);
       $languages = $this->languageManager->getLanguages();
-      $languageName = isset($languages[$language->id]) ? $languages[$language->id]->name : '';
-      $filename = $language->id .'.po';
+      $languageName = isset($languages[$language->getId()]) ? $languages[$language->getId()]->getName() : '';
+      $filename = $language->getId() .'.po';
     }
     else {
       // Template required.
diff --git a/core/modules/locale/lib/Drupal/locale/Form/ImportForm.php b/core/modules/locale/lib/Drupal/locale/Form/ImportForm.php
index 21b3150..e22cb52 100644
--- a/core/modules/locale/lib/Drupal/locale/Form/ImportForm.php
+++ b/core/modules/locale/lib/Drupal/locale/Form/ImportForm.php
@@ -81,7 +81,7 @@ public function buildForm(array $form, array &$form_state) {
     $existing_languages = array();
     foreach ($languages as $langcode => $language) {
       if ($langcode != 'en' || locale_translate_english()) {
-        $existing_languages[$langcode] = $language->name;
+        $existing_languages[$langcode] = $language->getName();
       }
     }
 
@@ -179,7 +179,7 @@ public function submitForm(array &$form, array &$form_state) {
         'id' => $form_state['values']['langcode']
       ));
       $language = language_save($language);
-      drupal_set_message($this->t('The language %language has been created.', array('%language' => $this->t($language->name))));
+      drupal_set_message($this->t('The language %language has been created.', array('%language' => $this->t($language->getName()))));
     }
     $options = array(
       'langcode' => $form_state['values']['langcode'],
diff --git a/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php b/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php
index c846026..24066a4 100644
--- a/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php
+++ b/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php
@@ -33,7 +33,7 @@ public function buildForm(array $form, array &$form_state) {
     $this->languageManager->reset();
     $languages = language_list();
 
-    $langname = isset($langcode) ? $languages[$langcode]->name : "- None -";
+    $langname = isset($langcode) ? $languages[$langcode]->getName() : "- None -";
 
     $form['#attached']['library'][] = 'locale/drupal.locale.admin';
 
diff --git a/core/modules/locale/lib/Drupal/locale/Form/TranslateFormBase.php b/core/modules/locale/lib/Drupal/locale/Form/TranslateFormBase.php
index 24b378e..9d1a4d1 100644
--- a/core/modules/locale/lib/Drupal/locale/Form/TranslateFormBase.php
+++ b/core/modules/locale/lib/Drupal/locale/Form/TranslateFormBase.php
@@ -8,7 +8,6 @@
 namespace Drupal\locale\Form;
 
 use Drupal\Core\Form\FormBase;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\locale\StringStorageInterface;
 use Drupal\Core\State\StateInterface;
@@ -166,12 +165,12 @@ protected function translateFilters() {
     $language_options = array();
     foreach ($languages as $langcode => $language) {
       if ($langcode != 'en' || locale_translate_english()) {
-        $language_options[$langcode] = $language->name;
+        $language_options[$langcode] = $language->getName();
       }
     }
 
     // Pick the current interface language code for the filter.
-    $default_langcode = $this->languageManager->getCurrentLanguage()->id;
+    $default_langcode = $this->languageManager->getCurrentLanguage()->getId();
     if (!isset($language_options[$default_langcode])) {
       $available_langcodes = array_keys($language_options);
       $default_langcode = array_shift($available_langcodes);
diff --git a/core/modules/locale/lib/Drupal/locale/LocaleConfigManager.php b/core/modules/locale/lib/Drupal/locale/LocaleConfigManager.php
index 3c0dc57..5ff5175 100644
--- a/core/modules/locale/lib/Drupal/locale/LocaleConfigManager.php
+++ b/core/modules/locale/lib/Drupal/locale/LocaleConfigManager.php
@@ -8,10 +8,10 @@
 namespace Drupal\locale;
 
 use Drupal\Core\Cache\CacheBackendInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Config\TypedConfigManager;
 use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Config\LanguageConfigFactoryOverrideInterface;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 
@@ -308,14 +308,14 @@ public function translateString($name, $langcode, $source, $context) {
    *
    * @param string $name
    *   Configuration name.
-   * @param \Drupal\Core\Language\Language $language
+   * @param \Drupal\Core\Language\LanguageInterface $language
    *   A language object.
    *
    * @return bool
    *   A boolean indicating if a language has configuration translations.
    */
-  public function hasTranslation($name, Language $language) {
-    $translation = $this->languageManager->getLanguageConfigOverride($language->id, $name);
+  public function hasTranslation($name, LanguageInterface $language) {
+    $translation = $this->languageManager->getLanguageConfigOverride($language->getId(), $name);
     return !$translation->isNew();
   }
 
diff --git a/core/modules/locale/lib/Drupal/locale/LocaleTranslation.php b/core/modules/locale/lib/Drupal/locale/LocaleTranslation.php
index 63abc07..d9a9800 100644
--- a/core/modules/locale/lib/Drupal/locale/LocaleTranslation.php
+++ b/core/modules/locale/lib/Drupal/locale/LocaleTranslation.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\DestructableInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\Core\Lock\LockBackendInterface;
 use Drupal\Core\StringTranslation\Translator\TranslatorInterface;
@@ -101,7 +101,7 @@ public function __construct(StringStorageInterface $storage, CacheBackendInterfa
    */
   public function getStringTranslation($langcode, $string, $context) {
     // If the language is not suitable for locale module, just return.
-    if ($langcode == Language::LANGCODE_SYSTEM || ($langcode == 'en' && !$this->canTranslateEnglish())) {
+    if ($langcode == LanguageInterface::LANGCODE_SYSTEM || ($langcode == 'en' && !$this->canTranslateEnglish())) {
       return FALSE;
     }
     // Strings are cached by langcode, context and roles, using instances of the
diff --git a/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php b/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php
index c0095f1..dd24d99 100644
--- a/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php
+++ b/core/modules/locale/lib/Drupal/locale/LocaleTypedConfig.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\locale;
 
-use Drupal\Core\Language\Language;
 use Drupal\Core\TypedData\ContextAwareInterface;
 use Drupal\Core\Config\Schema\Element;
 use Drupal\Core\Config\Schema\ArrayElement;
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
index a4ee53a..8a630eb 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\locale\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 use Drupal\locale\LocaleTypedConfig;
 
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocalePathTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocalePathTest.php
index cae7f4b..ef99bec 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocalePathTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocalePathTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\locale\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -106,7 +106,7 @@ function testPathLanguageConfiguration() {
     $edit = array(
       'source'   => 'node/' . $node->id(),
       'alias'    => $custom_path,
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     );
     $this->container->get('path.alias_storage')->save($edit['source'], $edit['alias'], $edit['langcode']);
     $lookup_path = $this->container->get('path.alias_manager')->getAliasByPath('node/' . $node->id(), 'en');
@@ -118,21 +118,21 @@ function testPathLanguageConfiguration() {
 
     // Create language nodes to check priority of aliases.
     $first_node = $this->drupalCreateNode(array('type' => 'page', 'promote' => 1, 'langcode' => 'en'));
-    $second_node = $this->drupalCreateNode(array('type' => 'page', 'promote' => 1, 'langcode' => Language::LANGCODE_NOT_SPECIFIED));
+    $second_node = $this->drupalCreateNode(array('type' => 'page', 'promote' => 1, 'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED));
 
     // Assign a custom path alias to the first node with the English language.
     $edit = array(
       'source'   => 'node/' . $first_node->id(),
       'alias'    => $custom_path,
-      'langcode' => $first_node->language()->id,
+      'langcode' => $first_node->language()->getId(),
     );
     $this->container->get('path.alias_storage')->save($edit['source'], $edit['alias'], $edit['langcode']);
 
-    // Assign a custom path alias to second node with Language::LANGCODE_NOT_SPECIFIED.
+    // Assign a custom path alias to second node with LanguageInterface::LANGCODE_NOT_SPECIFIED.
     $edit = array(
       'source'   => 'node/' . $second_node->id(),
       'alias'    => $custom_path,
-      'langcode' => $second_node->language()->id,
+      'langcode' => $second_node->language()->getId(),
     );
     $this->container->get('path.alias_storage')->save($edit['source'], $edit['alias'], $edit['langcode']);
 
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleStringTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleStringTest.php
index a9b45ec..151a40f 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleStringTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleStringTest.php
@@ -193,8 +193,10 @@ function buildSourceString($values = array()) {
    */
   function createAllTranslations($source, $values = array()) {
     $list = array();
-    foreach ($this->container->get('language_manager')->getLanguages() as $language) {
-      $list[$language->id] = $this->createTranslation($source, $language->id, $values);
+    /** @var \Drupal\Core\Language\LanguageManagerInterface $language_manager */
+    $language_manager = $this->container->get('language_manager');
+    foreach ($language_manager->getLanguages() as $language) {
+      $list[$language->getId()] = $this->createTranslation($source, $language->getId(), $values);
     }
     return $list;
   }
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
index fa33010..33051f9 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\locale\Tests;
 
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
 use Drupal\Component\Utility\String;
@@ -152,7 +153,7 @@ function testStringTranslation() {
     $this->container->get('string_translation')->reset();
     // Now we should get the proper fresh translation from t().
     $this->assertTrue($name != $translation_to_en && t($name, array(), array('langcode' => 'en')) == $translation_to_en, 't() works for English.');
-    $this->assertTrue(t($name, array(), array('langcode' => Language::LANGCODE_SYSTEM)) == $name, 't() works for Language::LANGCODE_SYSTEM.');
+    $this->assertTrue(t($name, array(), array('langcode' => LanguageInterface::LANGCODE_SYSTEM)) == $name, 't() works for LanguageInterface::LANGCODE_SYSTEM.');
 
     $search = array(
       'string' => $name,
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index 06c0887..0ccb4cd 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -6,7 +6,7 @@
  */
 
 use Drupal\locale\Gettext;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\file\FileInterface;
 
 /**
@@ -167,7 +167,7 @@ function locale_translate_batch_build($files, $options) {
  *
  * @param object $file
  *   A file object of the gettext file to be imported. The file object must
- *   contain a language parameter (other than Language::LANGCODE_NOT_SPECIFIED). This
+ *   contain a language parameter (other than LanguageInterface::LANGCODE_NOT_SPECIFIED). This
  *   is used as the language of the import.
  *
  * @param array $options
@@ -192,7 +192,7 @@ function locale_translate_batch_import($file, $options, &$context) {
     'customized' => LOCALE_NOT_CUSTOMIZED,
   );
 
-  if (isset($file->langcode) && $file->langcode != Language::LANGCODE_NOT_SPECIFIED) {
+  if (isset($file->langcode) && $file->langcode != LanguageInterface::LANGCODE_NOT_SPECIFIED) {
 
     try {
       if (empty($context['sandbox'])) {
@@ -459,7 +459,7 @@ function locale_translate_file_attach_properties($file, $options = array()) {
     $file->langcode = isset($options['langcode']) ? $options['langcode'] : $matches[5];
   }
   else {
-    $file->langcode = Language::LANGCODE_NOT_SPECIFIED;
+    $file->langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
   }
   return $file;
 }
diff --git a/core/modules/locale/locale.install b/core/modules/locale/locale.install
index c62c842..29c0657 100644
--- a/core/modules/locale/locale.install
+++ b/core/modules/locale/locale.install
@@ -5,7 +5,6 @@
  * Install, update, and uninstall functions for the Locale module.
  */
 
-use Drupal\Core\Language\Language;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationSelected;
 
 /**
diff --git a/core/modules/locale/locale.module b/core/modules/locale/locale.module
index d3e05dc..97bb3a9 100644
--- a/core/modules/locale/locale.module
+++ b/core/modules/locale/locale.module
@@ -14,7 +14,7 @@
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Entity\Language as LanguageEntity;
 use Drupal\Component\Utility\Crypt;
 use Symfony\Component\HttpFoundation\Request;
@@ -303,7 +303,7 @@ function locale_get_plural($count, $langcode = NULL) {
   // individually for each language.
   $plural_indexes = &drupal_static(__FUNCTION__ . ':plurals', array());
 
-  $langcode = $langcode ? $langcode : $language_interface->id;
+  $langcode = $langcode ? $langcode : $language_interface->getId();
 
   if (!isset($plural_indexes[$langcode][$count])) {
     // Retrieve and statically cache the plural formulas for all languages.
@@ -590,11 +590,11 @@ function locale_js_translate(array $files = array()) {
   }
 
   // If necessary, rebuild the translation file for the current language.
-  if (!empty($parsed['refresh:' . $language_interface->id])) {
+  if (!empty($parsed['refresh:' . $language_interface->getId()])) {
     // Don't clear the refresh flag on failure, so that another try will
     // be performed later.
     if (_locale_rebuild_js()) {
-      unset($parsed['refresh:' . $language_interface->id]);
+      unset($parsed['refresh:' . $language_interface->getId()]);
     }
     // Store any changes after refresh was attempted.
     \Drupal::state()->set('system.javascript_parsed', $parsed);
@@ -608,9 +608,9 @@ function locale_js_translate(array $files = array()) {
   // Add the translation JavaScript file to the page.
   $locale_javascripts = \Drupal::state()->get('locale.translation.javascript') ?: array();
   $translation_file = NULL;
-  if (!empty($files) && !empty($locale_javascripts[$language_interface->id])) {
+  if (!empty($files) && !empty($locale_javascripts[$language_interface->getId()])) {
     // Add the translation JavaScript file to the page.
-    $translation_file = $dir . '/' . $language_interface->id . '_' . $locale_javascripts[$language_interface->id] . '.js';
+    $translation_file = $dir . '/' . $language_interface->getId() . '_' . $locale_javascripts[$language_interface->getId()] . '.js';
   }
   return $translation_file;
 }
@@ -628,7 +628,7 @@ function locale_library_alter(array &$library, $name) {
 
     $language_interface = \Drupal::languageManager()->getCurrentLanguage();
     $settings['jquery']['ui']['datepicker'] = array(
-      'isRTL' => $language_interface->direction == Language::DIRECTION_RTL,
+      'isRTL' => $language_interface->getDirection() == LanguageInterface::DIRECTION_RTL,
       'firstDay' => \Drupal::config('system.date')->get('first_day'),
     );
     $library['js'][] = array(
@@ -801,20 +801,22 @@ function locale_system_file_system_settings_submit(&$form, $form_state) {
  * Implements hook_preprocess_HOOK() for node templates.
  */
 function locale_preprocess_node(&$variables) {
-  if ($variables['node']->language()->id != Language::LANGCODE_NOT_SPECIFIED) {
+  /** @var \Drupal\node\NodeInterface $node */
+  $node = $variables['node'];
+  if ($node->language()->getId() != LanguageInterface::LANGCODE_NOT_SPECIFIED) {
     $language_interface = \Drupal::languageManager()->getCurrentLanguage();
 
-    $node_language = $variables['node']->language();
-    if ($node_language->id != $language_interface->id) {
+    $node_language = $node->language();
+    if ($node_language->getId() != $language_interface->getId()) {
       // If the node language was different from the page language, we should
       // add markup to identify the language. Otherwise the page language is
       // inherited.
-      $variables['attributes']['lang'] = $node_language->id;
-      if ($node_language->direction != $language_interface->direction) {
+      $variables['attributes']['lang'] = $node_language->getId();
+      if ($node_language->getDirection() != $language_interface->getDirection()) {
         // If text direction is different form the page's text direction, add
         // direction information as well.
         $dir = array('ltr', 'rtl');
-        $variables['attributes']['dir'] = $dir[$node_language->direction];
+        $variables['attributes']['dir'] = $dir[$node_language->getDirection()];
       }
     }
   }
@@ -1266,7 +1268,7 @@ function _locale_rebuild_js($langcode = NULL) {
   // Only add strings with a translation to the translations array.
   $conditions = array(
     'type' => 'javascript',
-    'language' =>  $language->id,
+    'language' =>  $language->getId(),
     'translated' => TRUE,
   );
   $translations = array();
@@ -1283,8 +1285,8 @@ function _locale_rebuild_js($langcode = NULL) {
     );
 
     $locale_plurals = \Drupal::state()->get('locale.translation.plurals') ?: array();
-    if (!empty($locale_plurals[$language->id]['formula'])) {
-      $data['pluralFormula'] = $locale_plurals[$language->id]['formula'];
+    if (!empty($locale_plurals[$language->getId()]['formula'])) {
+      $data['pluralFormula'] = $locale_plurals[$language->getId()]['formula'];
     }
 
     $data = 'Drupal.locale = ' . Json::encode($data) . ';';
@@ -1297,23 +1299,23 @@ function _locale_rebuild_js($langcode = NULL) {
 
   // Delete old file, if we have no translations anymore, or a different file to be saved.
   $locale_javascripts = \Drupal::state()->get('locale.translation.javascript') ?: array();
-  $changed_hash = !isset($locale_javascripts[$language->id]) || ($locale_javascripts[$language->id] != $data_hash);
-  if (!empty($locale_javascripts[$language->id]) && (!$data || $changed_hash)) {
-    file_unmanaged_delete($dir . '/' . $language->id . '_' . $locale_javascripts[$language->id] . '.js');
-    $locale_javascripts[$language->id] = '';
+  $changed_hash = !isset($locale_javascripts[$language->getId()]) || ($locale_javascripts[$language->getId()] != $data_hash);
+  if (!empty($locale_javascripts[$language->getId()]) && (!$data || $changed_hash)) {
+    file_unmanaged_delete($dir . '/' . $language->getId() . '_' . $locale_javascripts[$language->getId()] . '.js');
+    $locale_javascripts[$language->getId()] = '';
     $status = 'deleted';
   }
 
   // Only create a new file if the content has changed or the original file got
   // lost.
-  $dest = $dir . '/' . $language->id . '_' . $data_hash . '.js';
+  $dest = $dir . '/' . $language->getId() . '_' . $data_hash . '.js';
   if ($data && ($changed_hash || !file_exists($dest))) {
     // Ensure that the directory exists and is writable, if possible.
     file_prepare_directory($dir, FILE_CREATE_DIRECTORY);
 
     // Save the file.
     if (file_unmanaged_save_data($data, $dest)) {
-      $locale_javascripts[$language->id] = $data_hash;
+      $locale_javascripts[$language->getId()] = $data_hash;
       // If we deleted a previous version of the file and we replace it with a
       // new one we have an update.
       if ($status == 'deleted') {
@@ -1331,7 +1333,7 @@ function _locale_rebuild_js($langcode = NULL) {
       }
     }
     else {
-      $locale_javascripts[$language->id] = '';
+      $locale_javascripts[$language->getId()] = '';
       $status = 'error';
     }
   }
@@ -1346,21 +1348,21 @@ function _locale_rebuild_js($langcode = NULL) {
   // Log the operation and return success flag.
   switch ($status) {
     case 'updated':
-      watchdog('locale', 'Updated JavaScript translation file for the language %language.', array('%language' => $language->name));
+      watchdog('locale', 'Updated JavaScript translation file for the language %language.', array('%language' => $language->getName()));
       return TRUE;
 
     case 'rebuilt':
-      watchdog('locale', 'JavaScript translation file %file.js was lost.', array('%file' => $locale_javascripts[$language->id]), WATCHDOG_WARNING);
+      watchdog('locale', 'JavaScript translation file %file.js was lost.', array('%file' => $locale_javascripts[$language->getId()]), WATCHDOG_WARNING);
     // Proceed to the 'created' case as the JavaScript translation file has
     // been created again.
     case 'created':
-      watchdog('locale', 'Created JavaScript translation file for the language %language.', array('%language' => $language->name));
+      watchdog('locale', 'Created JavaScript translation file for the language %language.', array('%language' => $language->getName()));
       return TRUE;
     case 'deleted':
-      watchdog('locale', 'Removed JavaScript translation file for the language %language because no translations currently exist for that language.', array('%language' => $language->name));
+      watchdog('locale', 'Removed JavaScript translation file for the language %language because no translations currently exist for that language.', array('%language' => $language->getName()));
       return TRUE;
     case 'error':
-      watchdog('locale', 'An error occurred during creation of the JavaScript translation file for the language %language.', array('%language' => $language->name), WATCHDOG_ERROR);
+      watchdog('locale', 'An error occurred during creation of the JavaScript translation file for the language %language.', array('%language' => $language->getName()), WATCHDOG_ERROR);
       return FALSE;
     default:
       // No operation needed.
diff --git a/core/modules/locale/locale.pages.inc b/core/modules/locale/locale.pages.inc
index c35e33a..f7f6111 100644
--- a/core/modules/locale/locale.pages.inc
+++ b/core/modules/locale/locale.pages.inc
@@ -6,7 +6,6 @@
  */
 
 use Drupal\Component\Utility\String;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Render\Element;
 use Drupal\locale\SourceString;
 use Drupal\locale\TranslationString;
@@ -92,7 +91,7 @@ function locale_translation_status_form($form, &$form_state) {
 
     // Build data options for the select table.
     foreach($updates as $langcode => $update) {
-      $title = String::checkPlain($languages[$langcode]->name);
+      $title = String::checkPlain($languages[$langcode]->getName());
       $locale_translation_update_info = array('#theme' => 'locale_translation_update_info');
       foreach (array('updates', 'not_found') as $update_status) {
         if (isset($update[$update_status])) {
diff --git a/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkForm.php b/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkForm.php
index c365dae..c3f1be2 100644
--- a/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkForm.php
+++ b/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkForm.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Entity\EntityForm;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Path\AliasManagerInterface;
 use Drupal\Core\Routing\UrlGenerator;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -181,7 +181,7 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#type' => 'language_select',
       '#title' => t('Language'),
-      '#languages' => Language::STATE_ALL,
+      '#languages' => LanguageInterface::STATE_ALL,
       '#default_value' => $default_langcode,
       '#access' => $language_show,
     );
diff --git a/core/modules/menu_link/lib/Drupal/menu_link/MenuTree.php b/core/modules/menu_link/lib/Drupal/menu_link/MenuTree.php
index adbf85d..e54abb8 100644
--- a/core/modules/menu_link/lib/Drupal/menu_link/MenuTree.php
+++ b/core/modules/menu_link/lib/Drupal/menu_link/MenuTree.php
@@ -155,7 +155,7 @@ public function buildAllData($menu_name, $link = NULL, $max_depth = NULL) {
     $mlid = isset($link['mlid']) ? $link['mlid'] : 0;
     // Generate a cache ID (cid) specific for this $menu_name, $link, $language,
     // and depth.
-    $cid = 'links:' . $menu_name . ':all:' . $mlid . ':' . $language_interface->id . ':' . (int) $max_depth;
+    $cid = 'links:' . $menu_name . ':all:' . $mlid . ':' . $language_interface->getId() . ':' . (int) $max_depth;
 
     if (!isset($this->menuFullTrees[$cid])) {
       // If the static variable doesn't have the data, check {cache_menu}.
@@ -218,7 +218,7 @@ public function buildPageData($menu_name, $max_depth = NULL, $only_active_trail
         $max_depth = min($max_depth, MENU_MAX_DEPTH);
       }
       // Generate a cache ID (cid) specific for this page.
-      $cid = 'links:' . $menu_name . ':page:' . $system_path . ':' . $language_interface->id . ':' . $page_not_403 . ':' . (int) $max_depth;
+      $cid = 'links:' . $menu_name . ':page:' . $system_path . ':' . $language_interface->getId() . ':' . $page_not_403 . ':' . (int) $max_depth;
       // If we are asked for the active trail only, and $menu_name has not been
       // built and cached for this page yet, then this likely means that it
       // won't be built anymore, as this function is invoked from
@@ -454,7 +454,7 @@ protected function doBuildTree($menu_name, array $parameters = array()) {
     if (isset($parameters['expanded'])) {
       sort($parameters['expanded']);
     }
-    $tree_cid = 'links:' . $menu_name . ':tree-data:' . $language_interface->id . ':' . hash('sha256', serialize($parameters));
+    $tree_cid = 'links:' . $menu_name . ':tree-data:' . $language_interface->getId() . ':' . hash('sha256', serialize($parameters));
 
     // If we do not have this tree in the static cache, check {cache_menu}.
     if (!isset($this->menuTree[$tree_cid])) {
diff --git a/core/modules/menu_ui/lib/Drupal/menu_ui/MenuForm.php b/core/modules/menu_ui/lib/Drupal/menu_ui/MenuForm.php
index a796f66..6b5333c 100644
--- a/core/modules/menu_ui/lib/Drupal/menu_ui/MenuForm.php
+++ b/core/modules/menu_ui/lib/Drupal/menu_ui/MenuForm.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\Query\QueryFactory;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Render\Element;
 use Drupal\menu_link\MenuLinkStorageInterface;
 use Drupal\menu_link\MenuTreeInterface;
@@ -117,7 +117,7 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#type' => 'language_select',
       '#title' => t('Menu language'),
-      '#languages' => Language::STATE_ALL,
+      '#languages' => LanguageInterface::STATE_ALL,
       '#default_value' => $menu->langcode,
     );
     // Unlike the menu langcode, the default language configuration for menu
diff --git a/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuLanguageTest.php b/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuLanguageTest.php
index 73374aa..9e6f519 100644
--- a/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuLanguageTest.php
+++ b/core/modules/menu_ui/lib/Drupal/menu_ui/Tests/MenuLanguageTest.php
@@ -180,7 +180,7 @@ function testMenuLanguageRemovedEnglish() {
     // Remove English language. To do that another language has to be set as
     // default.
     $language = language_load('cs');
-    $language->default = TRUE;
+    $language->setDefault(TRUE);
     language_save($language);
     language_delete('en');
 
diff --git a/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/MachineName.php b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/MachineName.php
index 80532bc..9af3fdc 100644
--- a/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/MachineName.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/MachineName.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\migrate\Plugin\migrate\process;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\migrate\ProcessPluginBase;
 use Drupal\migrate\MigrateExecutable;
 use Drupal\migrate\Row;
@@ -34,7 +34,7 @@ class MachineName extends ProcessPluginBase {
    * {@inheritdoc}
    */
   public function transform($value, MigrateExecutable $migrate_executable, Row $row, $destination_property) {
-    $new_value = $this->getTransliteration()->transliterate($value, Language::LANGCODE_DEFAULT, '_');
+    $new_value = $this->getTransliteration()->transliterate($value, LanguageInterface::LANGCODE_DEFAULT, '_');
     $new_value = strtolower($new_value);
     $new_value = preg_replace('/[^a-z0-9_]+/', '_', $new_value);
     return preg_replace('/_+/', '_', $new_value);
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorFeedTest.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorFeedTest.php
index 1110f72..3b4cfc2 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorFeedTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorFeedTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\migrate_drupal\Tests\d6;
 
 use Drupal\aggregator\Entity\Feed;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\migrate\MigrateExecutable;
 use Drupal\migrate_drupal\Tests\MigrateDrupalTestBase;
 
@@ -52,7 +52,7 @@ public function testAggregatorFeedImport() {
     $feed = entity_load('aggregator_feed', 5);
     $this->assertNotNull($feed->uuid());
     $this->assertEqual($feed->title->value, 'Know Your Meme');
-    $this->assertEqual($feed->language()->id, Language::LANGCODE_NOT_SPECIFIED);
+    $this->assertEqual($feed->language()->getId(), LanguageInterface::LANGCODE_NOT_SPECIFIED);
     $this->assertEqual($feed->url->value, 'http://knowyourmeme.com/newsfeed.rss');
     $this->assertEqual($feed->refresh->value, 900);
     $this->assertEqual($feed->checked->value, 1387659487);
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorItemTest.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorItemTest.php
index c5ca816..c08890b 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorItemTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateAggregatorItemTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\migrate_drupal\Tests\d6;
 
 use Drupal\aggregator\Entity\Item;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\migrate\MigrateExecutable;
 use Drupal\migrate_drupal\Tests\MigrateDrupalTestBase;
 
@@ -76,7 +76,7 @@ public function testAggregatorItem() {
     $this->assertEqual($item->getDescription(), "<h2 id='new'>What's new with Drupal 8?</h2>");
     $this->assertEqual($item->getLink(), 'https://groups.drupal.org/node/395218');
     $this->assertEqual($item->getPostedTime(), 1389297196);
-    $this->assertEqual($item->language()->id, Language::LANGCODE_NOT_SPECIFIED);
+    $this->assertEqual($item->language()->getId(), LanguageInterface::LANGCODE_NOT_SPECIFIED);
     $this->assertEqual($item->getGuid(), '395218 at https://groups.drupal.org');
 
   }
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCommentTest.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCommentTest.php
index 409f6d2..03acbed 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCommentTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCommentTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\migrate_drupal\Tests\d6;
 
 use Drupal\comment\Entity\Comment;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\migrate\MigrateExecutable;
 use Drupal\migrate_drupal\Tests\MigrateDrupalTestBase;
 
@@ -76,7 +76,7 @@ public function testComments() {
     $this->assertEqual(0, $comment->pid->value);
     $this->assertEqual(1, $comment->entity_id->value);
     $this->assertEqual('node', $comment->entity_type->value);
-    $this->assertEqual(Language::LANGCODE_NOT_SPECIFIED, $comment->language()->id);
+    $this->assertEqual(LanguageInterface::LANGCODE_NOT_SPECIFIED, $comment->language()->getId());
 
     $comment = entity_load('comment', 2);
     $this->assertEqual('The response to the second comment.', $comment->subject->value);
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCustomBlockTest.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCustomBlockTest.php
index d48acaf..49edd03 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCustomBlockTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateCustomBlockTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\migrate_drupal\Tests\d6;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\custom_block\Entity\CustomBlock;
 use Drupal\migrate\MigrateExecutable;
 use Drupal\migrate_drupal\Tests\MigrateDrupalTestBase;
@@ -59,7 +59,7 @@ public function testBlockMigration() {
     $this->assertEqual('My block 1', $block->label());
     $this->assertEqual(1, $block->getRevisionId());
     $this->assertTrue(REQUEST_TIME <= $block->getChangedTime() && $block->getChangedTime() <= time());
-    $this->assertEqual(Language::LANGCODE_NOT_SPECIFIED, $block->language()->id);
+    $this->assertEqual(LanguageInterface::LANGCODE_NOT_SPECIFIED, $block->language()->getId());
     $this->assertEqual('<h3>My first custom block body</h3>', $block->body->value);
     $this->assertEqual('full_html', $block->body->format);
 
@@ -67,7 +67,7 @@ public function testBlockMigration() {
     $this->assertEqual('My block 2', $block->label());
     $this->assertEqual(2, $block->getRevisionId());
     $this->assertTrue(REQUEST_TIME <= $block->getChangedTime() && $block->getChangedTime() <= time());
-    $this->assertEqual(Language::LANGCODE_NOT_SPECIFIED, $block->language()->id);
+    $this->assertEqual(LanguageInterface::LANGCODE_NOT_SPECIFIED, $block->language()->getId());
     $this->assertEqual('<h3>My second custom block body</h3>', $block->body->value);
     $this->assertEqual('full_html', $block->body->format);
   }
diff --git a/core/modules/node/lib/Drupal/node/Access/NodeRevisionAccessCheck.php b/core/modules/node/lib/Drupal/node/Access/NodeRevisionAccessCheck.php
index 66dc7e2..06da782 100644
--- a/core/modules/node/lib/Drupal/node/Access/NodeRevisionAccessCheck.php
+++ b/core/modules/node/lib/Drupal/node/Access/NodeRevisionAccessCheck.php
@@ -127,7 +127,7 @@ public function checkAccess(NodeInterface $node, AccountInterface $account, $op
 
     // If no language code was provided, default to the node revision's langcode.
     if (empty($langcode)) {
-      $langcode = $node->language()->id;
+      $langcode = $node->language()->getId();
     }
 
     // Statically cache access by revision ID, language code, user account ID,
diff --git a/core/modules/node/lib/Drupal/node/Controller/NodeController.php b/core/modules/node/lib/Drupal/node/Controller/NodeController.php
index ccc3037..7874ebf 100644
--- a/core/modules/node/lib/Drupal/node/Controller/NodeController.php
+++ b/core/modules/node/lib/Drupal/node/Controller/NodeController.php
@@ -70,7 +70,7 @@ public function add(NodeTypeInterface $node_type) {
       'uid' => $account->id(),
       'name' => $account->getUsername() ?: '',
       'type' => $node_type->type,
-      'langcode' => $langcode ? $langcode : $this->languageManager()->getCurrentLanguage()->id,
+      'langcode' => $langcode ? $langcode : $this->languageManager()->getCurrentLanguage()->getId(),
     ));
 
     $form = $this->entityFormBuilder()->getForm($node);
diff --git a/core/modules/node/lib/Drupal/node/Entity/Node.php b/core/modules/node/lib/Drupal/node/Entity/Node.php
index 1d21504..ede6ed7 100644
--- a/core/modules/node/lib/Drupal/node/Entity/Node.php
+++ b/core/modules/node/lib/Drupal/node/Entity/Node.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Field\FieldDefinition;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\node\NodeInterface;
 use Drupal\user\UserInterface;
@@ -156,14 +156,14 @@ public function access($operation = 'view', AccountInterface $account = NULL) {
    * {@inheritdoc}
    */
   public function prepareLangcode() {
-    $langcode = $this->language()->id;
+    $langcode = $this->language()->getId();
     // If the Language module is enabled, try to use the language from content
     // negotiation.
     if (\Drupal::moduleHandler()->moduleExists('language')) {
       // Load languages the node exists in.
       $node_translations = $this->getTranslationLanguages();
       // Load the language from content negotiation.
-      $content_negotiation_langcode = \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT)->id;
+      $content_negotiation_langcode = \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();
       // If there is a translation available, use it.
       if (isset($node_translations[$content_negotiation_langcode])) {
         $langcode = $content_negotiation_langcode;
diff --git a/core/modules/node/lib/Drupal/node/NodeAccessController.php b/core/modules/node/lib/Drupal/node/NodeAccessController.php
index 7b85600..6c058ad 100644
--- a/core/modules/node/lib/Drupal/node/NodeAccessController.php
+++ b/core/modules/node/lib/Drupal/node/NodeAccessController.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Database\Query\SelectInterface;
 use Drupal\Core\Entity\EntityControllerInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Entity\EntityAccessController;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\ContentEntityBase;
@@ -58,7 +58,7 @@ public static function createInstance(ContainerInterface $container, EntityTypeI
   /**
    * {@inheritdoc}
    */
-  public function access(EntityInterface $entity, $operation, $langcode = Language::LANGCODE_DEFAULT, AccountInterface $account = NULL) {
+  public function access(EntityInterface $entity, $operation, $langcode = LanguageInterface::LANGCODE_DEFAULT, AccountInterface $account = NULL) {
     if (user_access('bypass node access', $account)) {
       return TRUE;
     }
diff --git a/core/modules/node/lib/Drupal/node/NodeForm.php b/core/modules/node/lib/Drupal/node/NodeForm.php
index 37bb7da..06d0070 100644
--- a/core/modules/node/lib/Drupal/node/NodeForm.php
+++ b/core/modules/node/lib/Drupal/node/NodeForm.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Entity\ContentEntityForm;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Component\Utility\String;
 
 /**
@@ -89,8 +89,8 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#title' => t('Language'),
       '#type' => 'language_select',
-      '#default_value' => $node->getUntranslated()->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#default_value' => $node->getUntranslated()->language()->getId(),
+      '#languages' => LanguageInterface::STATE_ALL,
       '#access' => isset($language_configuration['language_show']) && $language_configuration['language_show'],
     );
 
diff --git a/core/modules/node/lib/Drupal/node/NodeGrantDatabaseStorage.php b/core/modules/node/lib/Drupal/node/NodeGrantDatabaseStorage.php
index 9503713..8d34418 100644
--- a/core/modules/node/lib/Drupal/node/NodeGrantDatabaseStorage.php
+++ b/core/modules/node/lib/Drupal/node/NodeGrantDatabaseStorage.php
@@ -190,7 +190,7 @@ public function write(NodeInterface $node, array $grants, $realm = NULL, $delete
             $grant['nid'] = $node->id();
             $grant['langcode'] = $grant_langcode;
             // The record with the original langcode is used as the fallback.
-            if ($grant['langcode'] == $node->language()->id) {
+            if ($grant['langcode'] == $node->language()->getId()) {
               $grant['fallback'] = 1;
             }
             else {
diff --git a/core/modules/node/lib/Drupal/node/NodeListBuilder.php b/core/modules/node/lib/Drupal/node/NodeListBuilder.php
index fc9c0ba..1c3fafd 100644
--- a/core/modules/node/lib/Drupal/node/NodeListBuilder.php
+++ b/core/modules/node/lib/Drupal/node/NodeListBuilder.php
@@ -13,7 +13,7 @@
 use Drupal\Core\Entity\EntityListBuilder;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
@@ -96,10 +96,10 @@ public function buildRow(EntityInterface $entity) {
       '#theme' => 'mark',
       '#mark_type' => node_mark($entity->id(), $entity->getChangedTime()),
     );
-    $langcode = $entity->language()->id;
+    $langcode = $entity->language()->getId();
     $uri = $entity->urlInfo();
     $options = $uri->getOptions();
-    $options += ($langcode != Language::LANGCODE_NOT_SPECIFIED && isset($languages[$langcode]) ? array('language' => $languages[$langcode]) : array());
+    $options += ($langcode != LanguageInterface::LANGCODE_NOT_SPECIFIED && isset($languages[$langcode]) ? array('language' => $languages[$langcode]) : array());
     $uri->setOptions($options);
     $row['title']['data'] = array(
       '#type' => 'link',
diff --git a/core/modules/node/lib/Drupal/node/NodeViewBuilder.php b/core/modules/node/lib/Drupal/node/NodeViewBuilder.php
index 494183f..85fc50d 100644
--- a/core/modules/node/lib/Drupal/node/NodeViewBuilder.php
+++ b/core/modules/node/lib/Drupal/node/NodeViewBuilder.php
@@ -58,7 +58,7 @@ public function buildComponents(array &$build, array $entities, array $displays,
         $build[$id]['langcode'] = array(
           '#type' => 'item',
           '#title' => t('Language'),
-          '#markup' => $entity->language()->name,
+          '#markup' => $entity->language()->getName(),
           '#prefix' => '<div id="field-language-display">',
           '#suffix' => '</div>'
         );
diff --git a/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php b/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php
index 1bcd79b..bb7255e 100644
--- a/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php
+++ b/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php
@@ -13,7 +13,7 @@
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\State\StateInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Access\AccessibleInterface;
 use Drupal\Core\Database\Query\Condition;
@@ -287,7 +287,7 @@ public function execute() {
         'extra' => $extra,
         'score' => $item->calculated_score,
         'snippet' => search_excerpt($keys, $node->rendered, $item->langcode),
-        'langcode' => $node->language()->id,
+        'langcode' => $node->language()->getId(),
       );
     }
     return $results;
@@ -351,23 +351,23 @@ protected function indexNode(NodeInterface $node) {
     $node_render = $this->entityManager->getViewBuilder('node');
 
     foreach ($languages as $language) {
-      $node = $node->getTranslation($language->id);
+      $node = $node->getTranslation($language->getId());
       // Render the node.
-      $build = $node_render->view($node, 'search_index', $language->id);
+      $build = $node_render->view($node, 'search_index', $language->getId());
 
       unset($build['#theme']);
       $node->rendered = drupal_render($build);
 
-      $text = '<h1>' . check_plain($node->label($language->id)) . '</h1>' . $node->rendered;
+      $text = '<h1>' . check_plain($node->label($language->getId())) . '</h1>' . $node->rendered;
 
       // Fetch extra data normally not visible.
-      $extra = $this->moduleHandler->invokeAll('node_update_index', array($node, $language->id));
+      $extra = $this->moduleHandler->invokeAll('node_update_index', array($node, $language->getId()));
       foreach ($extra as $t) {
         $text .= $t;
       }
 
       // Update index.
-      search_index($node->id(), $this->getPluginId(), $text, $language->id);
+      search_index($node->id(), $this->getPluginId(), $text, $language->getId());
     }
   }
 
@@ -452,10 +452,10 @@ public function searchFormAlter(array &$form, array &$form_state) {
 
     // Add languages.
     $language_options = array();
-    $language_list = \Drupal::languageManager()->getLanguages(Language::STATE_ALL);
+    $language_list = \Drupal::languageManager()->getLanguages(LanguageInterface::STATE_ALL);
     foreach ($language_list as $langcode => $language) {
       // Make locked languages appear special in the list.
-      $language_options[$langcode] = $language->locked ? t('- @name -', array('@name' => $language->name)) : $language->name;
+      $language_options[$langcode] = $language->isLocked() ? t('- @name -', array('@name' => $language->getName())) : $language->getName();
     }
     if (count($language_options) > 1) {
       $form['advanced']['lang-fieldset'] = array(
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeAccessLanguageTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeAccessLanguageTest.php
index feeae45..e90b48b 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeAccessLanguageTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeAccessLanguageTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\node\Tests;
 
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Verifies node access functionality for multiple languages.
@@ -65,7 +66,7 @@ function testNodeAccess() {
     // Creating a public node with langcode Hungarian, will be saved as the
     // fallback in node access table.
     $node_public_hu = $this->drupalCreateNode(array('body' => array(array()), 'langcode' => 'hu', 'private' => FALSE));
-    $this->assertTrue($node_public_hu->language()->id == 'hu', 'Node created as Hungarian.');
+    $this->assertTrue($node_public_hu->language()->getId() == 'hu', 'Node created as Hungarian.');
 
     // Tests the default access is provided for the public Hungarian node.
     $this->assertNodeAccess($expected_node_access, $node_public_hu, $web_user);
@@ -82,7 +83,7 @@ function testNodeAccess() {
     // Creating a public node with no special langcode, like when no language
     // module enabled.
     $node_public_no_language = $this->drupalCreateNode(array('private' => FALSE));
-    $this->assertTrue($node_public_no_language->language()->id == Language::LANGCODE_NOT_SPECIFIED, 'Node created with not specified language.');
+    $this->assertTrue($node_public_no_language->language()->getId() == LanguageInterface::LANGCODE_NOT_SPECIFIED, 'Node created with not specified language.');
 
     // Tests that access is granted if requested with no language.
     $this->assertNodeAccess($expected_node_access, $node_public_no_language, $web_user);
@@ -100,7 +101,7 @@ function testNodeAccess() {
     \Drupal::entityManager()->getAccessController('node')->resetCache();
     \Drupal::state()->set('node_access_test_secret_catalan', 1);
     $node_public_ca = $this->drupalCreateNode(array('body' => array(array()), 'langcode' => 'ca', 'private' => FALSE));
-    $this->assertTrue($node_public_ca->language()->id == 'ca', 'Node created as Catalan.');
+    $this->assertTrue($node_public_ca->language()->getId() == 'ca', 'Node created as Catalan.');
 
     // Tests that access is granted if requested with no language.
     $this->assertNodeAccess($expected_node_access, $node_public_no_language, $web_user);
@@ -155,7 +156,7 @@ function testNodeAccessPrivate() {
     // Creating a private node with langcode Hungarian, will be saved as the
     // fallback in node access table.
     $node_private_hu = $this->drupalCreateNode(array('body' => array(array()), 'langcode' => 'hu', 'private' => TRUE));
-    $this->assertTrue($node_private_hu->language()->id == 'hu', 'Node created as Hungarian.');
+    $this->assertTrue($node_private_hu->language()->getId() == 'hu', 'Node created as Hungarian.');
 
     // Tests the default access is not provided for the private Hungarian node.
     $this->assertNodeAccess($expected_node_access_no_access, $node_private_hu, $web_user);
@@ -172,7 +173,7 @@ function testNodeAccessPrivate() {
     // Creating a private node with no special langcode, like when no language
     // module enabled.
     $node_private_no_language = $this->drupalCreateNode(array('private' => TRUE));
-    $this->assertTrue($node_private_no_language->language()->id == Language::LANGCODE_NOT_SPECIFIED, 'Node created with not specified language.');
+    $this->assertTrue($node_private_no_language->language()->getId() == LanguageInterface::LANGCODE_NOT_SPECIFIED, 'Node created with not specified language.');
 
     // Tests that access is not granted if requested with no language.
     $this->assertNodeAccess($expected_node_access_no_access, $node_private_no_language, $web_user);
@@ -203,7 +204,7 @@ function testNodeAccessPrivate() {
     // node_access_test_secret_catalan flag works.
     $private_ca_user = $this->drupalCreateUser(array('access content', 'node test view'));
     $node_private_ca = $this->drupalCreateNode(array('body' => array(array()), 'langcode' => 'ca', 'private' => TRUE));
-    $this->assertTrue($node_private_ca->language()->id == 'ca', 'Node created as Catalan.');
+    $this->assertTrue($node_private_ca->language()->getId() == 'ca', 'Node created as Catalan.');
 
     // Tests that Catalan is still not accessible to either user.
     $this->assertNodeAccess($expected_node_access_no_access, $node_private_ca, $web_user, 'ca');
@@ -235,17 +236,17 @@ function testNodeAccessQueryTag() {
     // Creating a private node with langcode Hungarian, will be saved as
     // the fallback in node access table.
     $node_private = $this->drupalCreateNode(array('body' => array(array()), 'langcode' => 'hu', 'private' => TRUE));
-    $this->assertTrue($node_private->language()->id == 'hu', 'Node created as Hungarian.');
+    $this->assertTrue($node_private->language()->getId() == 'hu', 'Node created as Hungarian.');
 
     // Creating a public node with langcode Hungarian, will be saved as
     // the fallback in node access table.
     $node_public = $this->drupalCreateNode(array('body' => array(array()), 'langcode' => 'hu', 'private' => FALSE));
-    $this->assertTrue($node_public->language()->id == 'hu', 'Node created as Hungarian.');
+    $this->assertTrue($node_public->language()->getId() == 'hu', 'Node created as Hungarian.');
 
     // Creating a public node with no special langcode, like when no language
     // module enabled.
     $node_no_language = $this->drupalCreateNode(array('private' => FALSE));
-    $this->assertTrue($node_no_language->language()->id == Language::LANGCODE_NOT_SPECIFIED, 'Node created with not specified language.');
+    $this->assertTrue($node_no_language->language()->getId() == LanguageInterface::LANGCODE_NOT_SPECIFIED, 'Node created with not specified language.');
 
     // Query the nodes table as the web user with the node access tag and no
     // specific langcode.
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeAccessPagerTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeAccessPagerTest.php
index ee9f7cd..75a17c9 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeAccessPagerTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeAccessPagerTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\node\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\comment\CommentInterface;
 use Drupal\simpletest\WebTestBase;
 
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeCreationTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeCreationTest.php
index 540f952..62846cf 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeCreationTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeCreationTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\node\Tests;
 
 use Drupal\Core\Database\Database;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests creating and saving a node.
@@ -84,7 +84,7 @@ function testFailedPageCreation() {
       'uid'      => $this->loggedInUser->id(),
       'name'     => $this->loggedInUser->name,
       'type'     => 'page',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'title'    => 'testing_transaction_exception',
     );
 
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeFieldMultilingualTestCase.php b/core/modules/node/lib/Drupal/node/Tests/NodeFieldMultilingualTestCase.php
index fd83b93..5ff1160 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeFieldMultilingualTestCase.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeFieldMultilingualTestCase.php
@@ -8,6 +8,7 @@
 namespace Drupal\node\Tests;
 
 use Drupal\field\Entity\FieldConfig;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
@@ -86,7 +87,7 @@ function testMultilingualNodeForm() {
     // Check that the node exists in the database.
     $node = $this->drupalGetNodeByTitle($edit[$title_key]);
     $this->assertTrue($node, 'Node found in database.');
-    $this->assertTrue($node->language()->id == $langcode && $node->body->value == $body_value, 'Field language correctly set.');
+    $this->assertTrue($node->language()->getId() == $langcode && $node->body->value == $body_value, 'Field language correctly set.');
 
     // Change node language.
     $langcode = 'it';
@@ -98,10 +99,10 @@ function testMultilingualNodeForm() {
     $this->drupalPostForm(NULL, $edit, t('Save'));
     $node = $this->drupalGetNodeByTitle($edit[$title_key], TRUE);
     $this->assertTrue($node, 'Node found in database.');
-    $this->assertTrue($node->language()->id == $langcode && $node->body->value == $body_value, 'Field language correctly changed.');
+    $this->assertTrue($node->language()->getId() == $langcode && $node->body->value == $body_value, 'Field language correctly changed.');
 
     // Enable content language URL detection.
-    $this->container->get('language_negotiator')->saveConfiguration(Language::TYPE_CONTENT, array(LanguageNegotiationUrl::METHOD_ID => 0));
+    $this->container->get('language_negotiator')->saveConfiguration(LanguageInterface::TYPE_CONTENT, array(LanguageNegotiationUrl::METHOD_ID => 0));
 
     // Test multilingual field language fallback logic.
     $this->drupalGet("it/node/{$node->id()}");
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeLastChangedTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeLastChangedTest.php
index bf23498..6f804a5 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeLastChangedTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeLastChangedTest.php
@@ -49,7 +49,7 @@ function testNodeLastChanged() {
     $changed_timestamp = node_last_changed($node->id());
     $this->assertEqual($changed_timestamp, $node->getChangedTime(), 'Expected last changed timestamp returned.');
 
-    $changed_timestamp = node_last_changed($node->id(), $node->language()->id);
+    $changed_timestamp = node_last_changed($node->id(), $node->language()->getId());
     $this->assertEqual($changed_timestamp, $node->getChangedTime(), 'Expected last changed timestamp returned.');
   }
 }
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsAllTestCase.php b/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsAllTestCase.php
index abc6668..6ce4832 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsAllTestCase.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsAllTestCase.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\node\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests actions against revisions for user with access to all revisions.
  */
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsTest.php
index bcb62fc..78db6b9 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeRevisionsTest.php
@@ -7,8 +7,6 @@
 
 namespace Drupal\node\Tests;
 
-use Drupal\Core\Language\Language;
-
 /**
  * Tests the node revision functionality.
  */
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeTokenReplaceTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeTokenReplaceTest.php
index 717abcc..17a482d 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeTokenReplaceTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeTokenReplaceTest.php
@@ -76,14 +76,14 @@ function testNodeTokenReplacement() {
     $tests['[node:title]'] = check_plain($node->getTitle());
     $tests['[node:body]'] = $node->body->processed;
     $tests['[node:summary]'] = $node->body->summary_processed;
-    $tests['[node:langcode]'] = check_plain($node->language()->id);
+    $tests['[node:langcode]'] = check_plain($node->language()->getId());
     $tests['[node:url]'] = url('node/' . $node->id(), $url_options);
     $tests['[node:edit-url]'] = url('node/' . $node->id() . '/edit', $url_options);
     $tests['[node:author]'] = String::checkPlain($account->getUsername());
     $tests['[node:author:uid]'] = $node->getOwnerId();
     $tests['[node:author:name]'] = String::checkPlain($account->getUsername());
-    $tests['[node:created:since]'] = \Drupal::service('date')->formatInterval(REQUEST_TIME - $node->getCreatedTime(), 2, $this->languageInterface->id);
-    $tests['[node:changed:since]'] = \Drupal::service('date')->formatInterval(REQUEST_TIME - $node->getChangedTime(), 2, $this->languageInterface->id);
+    $tests['[node:created:since]'] = \Drupal::service('date')->formatInterval(REQUEST_TIME - $node->getCreatedTime(), 2, $this->languageInterface->getId());
+    $tests['[node:changed:since]'] = \Drupal::service('date')->formatInterval(REQUEST_TIME - $node->getChangedTime(), 2, $this->languageInterface->getId());
 
     // Test to make sure that we generated something for each token.
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
@@ -97,7 +97,7 @@ function testNodeTokenReplacement() {
     $tests['[node:title]'] = $node->getTitle();
     $tests['[node:body]'] = $node->body->value;
     $tests['[node:summary]'] = $node->body->summary;
-    $tests['[node:langcode]'] = $node->language()->id;
+    $tests['[node:langcode]'] = $node->language()->getId();
     $tests['[node:author:name]'] = $account->getUsername();
 
     foreach ($tests as $input => $expected) {
diff --git a/core/modules/node/lib/Drupal/node/Tests/PagePreviewTest.php b/core/modules/node/lib/Drupal/node/Tests/PagePreviewTest.php
index 48a8ea6..5137bbd 100644
--- a/core/modules/node/lib/Drupal/node/Tests/PagePreviewTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/PagePreviewTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\node\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests the node entity preview functionality.
@@ -47,7 +47,7 @@ function setUp() {
       'name' => $this->randomName(),
       'description' => $this->randomName(),
       'vid' => $this->randomName(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'help' => '',
     ));
     $vocabulary->save();
@@ -59,7 +59,7 @@ function setUp() {
       'name' => $this->randomName(),
       'description' => $this->randomName(),
       'vid' => $this->vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term->save();
 
diff --git a/core/modules/node/lib/Drupal/node/Tests/Views/RowPluginTest.php b/core/modules/node/lib/Drupal/node/Tests/Views/RowPluginTest.php
index a44a369..7d83d3a 100644
--- a/core/modules/node/lib/Drupal/node/Tests/Views/RowPluginTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/Views/RowPluginTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\node\Tests\Views;
 
-use Drupal\Core\Language\Language;
 use Drupal\views\Views;
 
 /**
diff --git a/core/modules/node/node.admin.inc b/core/modules/node/node.admin.inc
index b0a806d..2da5e05 100644
--- a/core/modules/node/node.admin.inc
+++ b/core/modules/node/node.admin.inc
@@ -5,7 +5,6 @@
  * Content administration and module settings user interface.
  */
 
-use Drupal\Core\Language\Language;
 use Drupal\node\NodeInterface;
 
 /**
diff --git a/core/modules/node/node.install b/core/modules/node/node.install
index b075d93..3fe7dc0 100644
--- a/core/modules/node/node.install
+++ b/core/modules/node/node.install
@@ -6,7 +6,6 @@
  */
 
 use Drupal\Component\Uuid\Uuid;
-use Drupal\Core\Language\Language;
 
 /**
  * Implements hook_requirements().
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index 71a1f38..8edb6d6 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -9,7 +9,6 @@
  */
 
 use Drupal\Component\Utility\Xss;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\Request;
@@ -1009,7 +1008,7 @@ function node_block_access(Block $block, $operation, AccountInterface $account,
  */
 function node_feed($nids = FALSE, $channel = array()) {
   global $base_url;
-  $language_content = \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT);
+  $language_content = \Drupal::languageManager()->getCurrentLanguage(\Drupal\Core\Language\LanguageInterface::TYPE_CONTENT);
   $rss_config = \Drupal::config('system.rss');
 
   if ($nids === FALSE) {
@@ -1063,7 +1062,7 @@ function node_feed($nids = FALSE, $channel = array()) {
     'title'       => \Drupal::config('system.site')->get('name'),
     'link'        => $base_url,
     'description' => $rss_config->get('channel.description'),
-    'language'    => $language_content->id
+    'language'    => $language_content->getId()
   );
   $channel_extras = array_diff_key($channel, $channel_defaults);
   $channel = array_merge($channel_defaults, $channel);
diff --git a/core/modules/node/node.tokens.inc b/core/modules/node/node.tokens.inc
index 8789047..5b3c8a2 100644
--- a/core/modules/node/node.tokens.inc
+++ b/core/modules/node/node.tokens.inc
@@ -5,7 +5,7 @@
  * Builds placeholder replacement tokens for node-related data.
  */
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Implements hook_token_info().
@@ -94,7 +94,7 @@ function node_tokens($type, $tokens, array $data = array(), array $options = arr
     $langcode = $options['langcode'];
   }
   else {
-    $langcode = Language::LANGCODE_DEFAULT;
+    $langcode = LanguageInterface::LANGCODE_DEFAULT;
   }
   $sanitize = !empty($options['sanitize']);
 
@@ -164,7 +164,7 @@ function node_tokens($type, $tokens, array $data = array(), array $options = arr
           break;
 
         case 'langcode':
-          $replacements[$original] = $sanitize ? check_plain($node->language()->id) : $node->language()->id;
+          $replacements[$original] = $sanitize ? check_plain($node->language()->getId()) : $node->language()->getId();
           break;
 
         case 'url':
diff --git a/core/modules/path/lib/Drupal/path/Form/AddForm.php b/core/modules/path/lib/Drupal/path/Form/AddForm.php
index a5b056b..aab238b 100644
--- a/core/modules/path/lib/Drupal/path/Form/AddForm.php
+++ b/core/modules/path/lib/Drupal/path/Form/AddForm.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\path\Form;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Provides the path add form.
@@ -28,7 +28,7 @@ protected function buildPath($pid) {
     return array(
       'source' => '',
       'alias' => '',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'pid' => NULL,
     );
   }
diff --git a/core/modules/path/lib/Drupal/path/Form/PathFormBase.php b/core/modules/path/lib/Drupal/path/Form/PathFormBase.php
index ca507d1..75f7cc4 100644
--- a/core/modules/path/lib/Drupal/path/Form/PathFormBase.php
+++ b/core/modules/path/lib/Drupal/path/Form/PathFormBase.php
@@ -8,7 +8,7 @@
 namespace Drupal\path\Form;
 
 use Drupal\Core\Form\FormBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Path\AliasManagerInterface;
 use Drupal\Core\Path\AliasStorageInterface;
 use Drupal\Core\Url;
@@ -102,14 +102,14 @@ public function buildForm(array $form, array &$form_state, $pid = NULL) {
       $languages = \Drupal::languageManager()->getLanguages();
       $language_options = array();
       foreach ($languages as $langcode => $language) {
-        $language_options[$langcode] = $language->name;
+        $language_options[$langcode] = $language->getName();
       }
 
       $form['langcode'] = array(
         '#type' => 'select',
         '#title' => $this->t('Language'),
         '#options' => $language_options,
-        '#empty_value' => Language::LANGCODE_NOT_SPECIFIED,
+        '#empty_value' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
         '#empty_option' => $this->t('- None -'),
         '#default_value' => $this->path['langcode'],
         '#weight' => -10,
@@ -141,7 +141,7 @@ public function validateForm(array &$form, array &$form_state) {
     $alias = $form_state['values']['alias'];
     // Language is only set if language.module is enabled, otherwise save for all
     // languages.
-    $langcode = isset($form_state['values']['langcode']) ? $form_state['values']['langcode'] : Language::LANGCODE_NOT_SPECIFIED;
+    $langcode = isset($form_state['values']['langcode']) ? $form_state['values']['langcode'] : LanguageInterface::LANGCODE_NOT_SPECIFIED;
 
     if ($this->aliasStorage->aliasExists($alias, $langcode, $source)) {
       $this->setFormError('alias', $form_state, t('The alias %alias is already in use in this language.', array('%alias' => $alias)));
@@ -164,7 +164,7 @@ public function submitForm(array &$form, array &$form_state) {
     $alias = $form_state['values']['alias'];
     // Language is only set if language.module is enabled, otherwise save for all
     // languages.
-    $langcode = isset($form_state['values']['langcode']) ? $form_state['values']['langcode'] : Language::LANGCODE_NOT_SPECIFIED;
+    $langcode = isset($form_state['values']['langcode']) ? $form_state['values']['langcode'] : LanguageInterface::LANGCODE_NOT_SPECIFIED;
 
     $this->aliasStorage->save($source, $alias, $langcode, $pid);
 
diff --git a/core/modules/path/lib/Drupal/path/Plugin/Field/FieldWidget/PathWidget.php b/core/modules/path/lib/Drupal/path/Plugin/Field/FieldWidget/PathWidget.php
index ac465d9..e416bc5 100644
--- a/core/modules/path/lib/Drupal/path/Plugin/Field/FieldWidget/PathWidget.php
+++ b/core/modules/path/lib/Drupal/path/Plugin/Field/FieldWidget/PathWidget.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\WidgetBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\Validator\ConstraintViolationInterface;
 
 /**
@@ -33,7 +33,7 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
     $path = array();
     if (!$entity->isNew()) {
       $conditions = array('source' => $entity->getSystemPath());
-      if ($items->getLangcode() != Language::LANGCODE_NOT_SPECIFIED) {
+      if ($items->getLangcode() != LanguageInterface::LANGCODE_NOT_SPECIFIED) {
         $conditions['langcode'] = $items->getLangcode();
       }
       $path = \Drupal::service('path.alias_storage')->load($conditions);
diff --git a/core/modules/path/path.module b/core/modules/path/path.module
index ab102a9..2378423 100644
--- a/core/modules/path/path.module
+++ b/core/modules/path/path.module
@@ -6,7 +6,6 @@
  */
 
 use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Field\FieldDefinition;
diff --git a/core/modules/quickedit/lib/Drupal/quickedit/Tests/EditorSelectionTest.php b/core/modules/quickedit/lib/Drupal/quickedit/Tests/EditorSelectionTest.php
index b84f3af..03ce968 100644
--- a/core/modules/quickedit/lib/Drupal/quickedit/Tests/EditorSelectionTest.php
+++ b/core/modules/quickedit/lib/Drupal/quickedit/Tests/EditorSelectionTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\quickedit\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\quickedit\Plugin\InPlaceEditorManager;
 use Drupal\quickedit\EditorSelector;
 
@@ -50,7 +50,7 @@ protected function setUp() {
    */
   protected function getSelectedEditor($entity_id, $field_name, $view_mode = 'default') {
     $entity = entity_load('entity_test', $entity_id, TRUE);
-    $items = $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get($field_name);
+    $items = $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get($field_name);
     $options = entity_get_display('entity_test', 'entity_test', $view_mode)->getComponent($field_name);
     return $this->editorSelector->getEditor($options['type'], $items);
   }
diff --git a/core/modules/quickedit/lib/Drupal/quickedit/Tests/MetadataGeneratorTest.php b/core/modules/quickedit/lib/Drupal/quickedit/Tests/MetadataGeneratorTest.php
index 3a07223..7418ec0 100644
--- a/core/modules/quickedit/lib/Drupal/quickedit/Tests/MetadataGeneratorTest.php
+++ b/core/modules/quickedit/lib/Drupal/quickedit/Tests/MetadataGeneratorTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\quickedit\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\quickedit\EditorSelector;
 use Drupal\quickedit\MetadataGenerator;
 use Drupal\quickedit\Plugin\InPlaceEditorManager;
@@ -102,7 +102,7 @@ public function testSimpleEntityType() {
     $entity = entity_load('entity_test', $this->entity->id());
 
     // Verify metadata for field 1.
-    $items_1 = $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get($field_1_name);
+    $items_1 = $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get($field_1_name);
     $metadata_1 = $this->metadataGenerator->generateFieldMetadata($items_1, 'default');
     $expected_1 = array(
       'access' => TRUE,
@@ -113,7 +113,7 @@ public function testSimpleEntityType() {
     $this->assertEqual($expected_1, $metadata_1, 'The correct metadata is generated for the first field.');
 
     // Verify metadata for field 2.
-    $items_2 = $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get($field_2_name);
+    $items_2 = $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get($field_2_name);
     $metadata_2 = $this->metadataGenerator->generateFieldMetadata($items_2, 'default');
     $expected_2 = array(
       'access' => TRUE,
@@ -175,7 +175,7 @@ public function testEditorWithCustomMetadata() {
     $entity = entity_load('entity_test', $this->entity->id());
 
     // Verify metadata.
-    $items = $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get($field_name);
+    $items = $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get($field_name);
     $metadata = $this->metadataGenerator->generateFieldMetadata($items, 'default');
     $expected = array(
       'access' => TRUE,
diff --git a/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditAutocompleteTermTest.php b/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditAutocompleteTermTest.php
index 15d8ca9..9bee3e1 100644
--- a/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditAutocompleteTermTest.php
+++ b/core/modules/quickedit/lib/Drupal/quickedit/Tests/QuickEditAutocompleteTermTest.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Serialization\Json;
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -211,7 +211,7 @@ protected function createTerm() {
       // Use the first available text format.
       'format' => $format->format,
       'vid' => $this->vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term->save();
     return $term;
diff --git a/core/modules/quickedit/tests/Drupal/quickedit/Tests/Access/EditEntityFieldAccessCheckTest.php b/core/modules/quickedit/tests/Drupal/quickedit/Tests/Access/EditEntityFieldAccessCheckTest.php
index d1b0228..9b01048 100644
--- a/core/modules/quickedit/tests/Drupal/quickedit/Tests/Access/EditEntityFieldAccessCheckTest.php
+++ b/core/modules/quickedit/tests/Drupal/quickedit/Tests/Access/EditEntityFieldAccessCheckTest.php
@@ -12,7 +12,7 @@
 use Drupal\quickedit\Access\EditEntityFieldAccessCheck;
 use Drupal\Tests\UnitTestCase;
 use Drupal\field\FieldConfigInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Entity\EntityInterface;
 
 /**
@@ -127,14 +127,14 @@ public function testAccess(EntityInterface $entity, FieldConfigInterface $field
       ->will($this->returnValue($field));
     $entity_with_field->expects($this->once())
       ->method('hasTranslation')
-      ->with(Language::LANGCODE_NOT_SPECIFIED)
+      ->with(LanguageInterface::LANGCODE_NOT_SPECIFIED)
       ->will($this->returnValue(TRUE));
 
     // Prepare the request to be valid.
     $request->attributes->set('entity_type', 'test_entity');
     $request->attributes->set('entity', $entity_with_field);
     $request->attributes->set('field_name', $field_name);
-    $request->attributes->set('langcode', Language::LANGCODE_NOT_SPECIFIED);
+    $request->attributes->set('langcode', LanguageInterface::LANGCODE_NOT_SPECIFIED);
 
     $account = $this->getMock('Drupal\Core\Session\AccountInterface');
     $access = $this->editAccessCheck->access($request, $field_name, $account);
diff --git a/core/modules/quickedit/tests/modules/quickedit_test.module b/core/modules/quickedit/tests/modules/quickedit_test.module
index 4d4606c..0a73b25 100644
--- a/core/modules/quickedit/tests/modules/quickedit_test.module
+++ b/core/modules/quickedit/tests/modules/quickedit_test.module
@@ -5,7 +5,7 @@
  * Helper module for the Quick Edit tests.
  */
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
 
@@ -21,7 +21,7 @@ function quickedit_test_entity_view_alter(&$build, EntityInterface $entity, Enti
       '#label_display' => 'Label',
       '#entity_type' => $entity->getEntityTypeId(),
       '#bundle' => $entity->bundle(),
-      '#language' => Language::LANGCODE_NOT_SPECIFIED,
+      '#language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       '#field_type' => 'pseudo',
       '#view_mode' => 'default',
       '#object' => $entity,
diff --git a/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php b/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php
index 5086bf1..e9a74a0 100644
--- a/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php
+++ b/core/modules/rdf/lib/Drupal/rdf/Tests/Field/TaxonomyTermReferenceRdfaTest.php
@@ -8,7 +8,7 @@
 
 use Drupal\rdf\Tests\Field\FieldRdfaTestBase;
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests the RDFa output of the taxonomy term reference field formatter.
@@ -55,7 +55,7 @@ public function setUp() {
     $vocabulary = entity_create('taxonomy_vocabulary', array(
       'name' => $this->randomName(),
       'vid' => drupal_strtolower($this->randomName()),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $vocabulary->save();
 
@@ -82,7 +82,7 @@ public function setUp() {
     $this->term = entity_create('taxonomy_term', array(
       'name' => $this->randomName(),
       'vid' => $vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $this->term->save();
 
diff --git a/core/modules/rdf/lib/Drupal/rdf/Tests/FileFieldAttributesTest.php b/core/modules/rdf/lib/Drupal/rdf/Tests/FileFieldAttributesTest.php
index cc738e4..2381395 100644
--- a/core/modules/rdf/lib/Drupal/rdf/Tests/FileFieldAttributesTest.php
+++ b/core/modules/rdf/lib/Drupal/rdf/Tests/FileFieldAttributesTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\rdf\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\file\Tests\FileFieldTestBase;
 
 /**
diff --git a/core/modules/rdf/lib/Drupal/rdf/Tests/ImageFieldAttributesTest.php b/core/modules/rdf/lib/Drupal/rdf/Tests/ImageFieldAttributesTest.php
index 14af8f6..39e52b7 100644
--- a/core/modules/rdf/lib/Drupal/rdf/Tests/ImageFieldAttributesTest.php
+++ b/core/modules/rdf/lib/Drupal/rdf/Tests/ImageFieldAttributesTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\rdf\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\image\Tests\ImageFieldTestBase;
 
 /**
diff --git a/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php b/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php
index 5d34845..fd68a994 100644
--- a/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php
+++ b/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageFieldDisplayTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\responsive_image\Tests;
 
-use Drupal\Core\Language\Language;
 use Drupal\breakpoint\Entity\Breakpoint;
 use Drupal\image\Tests\ImageFieldTestBase;
 
diff --git a/core/modules/rest/lib/Drupal/rest/Tests/ReadTest.php b/core/modules/rest/lib/Drupal/rest/Tests/ReadTest.php
index 15206f7..6777cf5 100644
--- a/core/modules/rest/lib/Drupal/rest/Tests/ReadTest.php
+++ b/core/modules/rest/lib/Drupal/rest/Tests/ReadTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\rest\Tests;
 
 use Drupal\Component\Serialization\Json;
-use Drupal\Core\Language\Language;
 use Drupal\rest\Tests\RESTTestBase;
 
 /**
diff --git a/core/modules/search/lib/Drupal/search/Tests/SearchMatchTest.php b/core/modules/search/lib/Drupal/search/Tests/SearchMatchTest.php
index 27b427d..14ea024 100644
--- a/core/modules/search/lib/Drupal/search/Tests/SearchMatchTest.php
+++ b/core/modules/search/lib/Drupal/search/Tests/SearchMatchTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\search\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 // The search index can contain different types of content. Typically the type
 // is 'node'. Here we test with _test_ and _test2_ as the type.
@@ -42,10 +42,10 @@ function _setup() {
     \Drupal::config('search.settings')->set('index.minimum_word_size', 3)->save();
 
     for ($i = 1; $i <= 7; ++$i) {
-      search_index($i, SEARCH_TYPE, $this->getText($i), Language::LANGCODE_NOT_SPECIFIED);
+      search_index($i, SEARCH_TYPE, $this->getText($i), LanguageInterface::LANGCODE_NOT_SPECIFIED);
     }
     for ($i = 1; $i <= 5; ++$i) {
-      search_index($i + 7, SEARCH_TYPE_2, $this->getText2($i), Language::LANGCODE_NOT_SPECIFIED);
+      search_index($i + 7, SEARCH_TYPE_2, $this->getText2($i), LanguageInterface::LANGCODE_NOT_SPECIFIED);
     }
     // No getText builder function for Japanese text; just a simple array.
     foreach (array(
@@ -53,7 +53,7 @@ function _setup() {
       14 => 'ドルーパルが大好きよ！',
       15 => 'コーヒーとケーキ',
     ) as $i => $jpn) {
-      search_index($i, SEARCH_TYPE_JPN, $jpn, Language::LANGCODE_NOT_SPECIFIED);
+      search_index($i, SEARCH_TYPE_JPN, $jpn, LanguageInterface::LANGCODE_NOT_SPECIFIED);
     }
     search_update_totals();
   }
diff --git a/core/modules/search/lib/Drupal/search/Tests/SearchNumberMatchingTest.php b/core/modules/search/lib/Drupal/search/Tests/SearchNumberMatchingTest.php
index f52a222..65d2bfd 100644
--- a/core/modules/search/lib/Drupal/search/Tests/SearchNumberMatchingTest.php
+++ b/core/modules/search/lib/Drupal/search/Tests/SearchNumberMatchingTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\search\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests that various number formats match each other in searching.
@@ -49,7 +49,7 @@ function setUp() {
       $info = array(
         'body' => array(array('value' => $num)),
         'type' => 'page',
-        'language' => Language::LANGCODE_NOT_SPECIFIED,
+        'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       );
       $this->nodes[] = $this->drupalCreateNode($info);
     }
diff --git a/core/modules/search/lib/Drupal/search/Tests/SearchNumbersTest.php b/core/modules/search/lib/Drupal/search/Tests/SearchNumbersTest.php
index 6275943..41a41ae 100644
--- a/core/modules/search/lib/Drupal/search/Tests/SearchNumbersTest.php
+++ b/core/modules/search/lib/Drupal/search/Tests/SearchNumbersTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\search\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests that numbers with different formats can be searched.
@@ -55,7 +55,7 @@ function setUp() {
       $info = array(
         'body' => array(array('value' => $num)),
         'type' => 'page',
-        'language' => Language::LANGCODE_NOT_SPECIFIED,
+        'language' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
         'title' => $doc . ' number',
       );
       $this->nodes[$doc] = $this->drupalCreateNode($info);
diff --git a/core/modules/search/search.pages.inc b/core/modules/search/search.pages.inc
index 34b235c..bc7ba1b 100644
--- a/core/modules/search/search.pages.inc
+++ b/core/modules/search/search.pages.inc
@@ -5,8 +5,6 @@
  * User page callbacks for the Search module.
  */
 
-use Drupal\Core\Language\Language;
-
 /**
  * Implements hook_theme_suggestions_HOOK().
  */
@@ -36,7 +34,7 @@ function template_preprocess_search_result(&$variables) {
   $result = $variables['result'];
   $variables['url'] = check_url($result['link']);
   $variables['title'] = check_plain($result['title']);
-  if (isset($result['language']) && $result['language'] != $language_interface->id && $result['language'] != Language::LANGCODE_NOT_SPECIFIED) {
+  if (isset($result['language']) && $result['language'] != $language_interface->getId() && $result['language'] != LanguageInterface::LANGCODE_NOT_SPECIFIED) {
     $variables['title_attributes']['lang'] = $result['language'];
     $variables['content_attributes']['lang'] = $result['language'];
   }
diff --git a/core/modules/serialization/lib/Drupal/serialization/Tests/EntitySerializationTest.php b/core/modules/serialization/lib/Drupal/serialization/Tests/EntitySerializationTest.php
index 865704d..d53502a 100644
--- a/core/modules/serialization/lib/Drupal/serialization/Tests/EntitySerializationTest.php
+++ b/core/modules/serialization/lib/Drupal/serialization/Tests/EntitySerializationTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\serialization\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\Serializer\Serializer;
 use Drupal\Component\Utility\String;
 
@@ -87,7 +87,7 @@ public function testNormalize() {
         array('value' => $this->entity->uuid()),
       ),
       'langcode' => array(
-        array('value' => Language::LANGCODE_NOT_SPECIFIED),
+        array('value' => LanguageInterface::LANGCODE_NOT_SPECIFIED),
       ),
       'default_langcode' => array(
         array('value' => NULL),
@@ -143,7 +143,7 @@ public function testSerialize() {
       'id' => '<id><value>' . $this->entity->id() . '</value></id>',
       'revision_id' => '<revision_id><value>' . $this->entity->getRevisionId() . '</value></revision_id>',
       'uuid' => '<uuid><value>' . $this->entity->uuid() . '</value></uuid>',
-      'langcode' => '<langcode><value>' . Language::LANGCODE_NOT_SPECIFIED . '</value></langcode>',
+      'langcode' => '<langcode><value>' . LanguageInterface::LANGCODE_NOT_SPECIFIED . '</value></langcode>',
       'default_langcode' => '<default_langcode><value/></default_langcode>',
       'name' => '<name><value>' . $this->values['name'] . '</value></name>',
       'type' => '<type><value>entity_test_mulrev</value></type>',
diff --git a/core/modules/shortcut/shortcut.install b/core/modules/shortcut/shortcut.install
index b7ed49c..8b87123 100644
--- a/core/modules/shortcut/shortcut.install
+++ b/core/modules/shortcut/shortcut.install
@@ -6,7 +6,6 @@
  */
 
 use Drupal\Core\Database\Database;
-use Drupal\Core\Language\Language;
 
 /**
  * Implements hook_schema().
diff --git a/core/modules/shortcut/src/ShortcutForm.php b/core/modules/shortcut/src/ShortcutForm.php
index 0e101ff..89606d1 100644
--- a/core/modules/shortcut/src/ShortcutForm.php
+++ b/core/modules/shortcut/src/ShortcutForm.php
@@ -8,7 +8,7 @@
 namespace Drupal\shortcut;
 
 use Drupal\Core\Entity\ContentEntityForm;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Form controller for the shortcut entity forms.
@@ -40,8 +40,8 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#title' => t('Language'),
       '#type' => 'language_select',
-      '#default_value' => $this->entity->getUntranslated()->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#default_value' => $this->entity->getUntranslated()->language()->getId(),
+      '#languages' => LanguageInterface::STATE_ALL,
     );
 
     return $form;
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 340b555..2518cda 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -16,7 +16,7 @@
 use Drupal\Core\Database\Database;
 use Drupal\Core\Database\ConnectionNotDefinedException;
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Session\AnonymousUserSession;
 use Drupal\Core\Session\UserSession;
@@ -251,7 +251,7 @@ function drupalGetNodeByTitle($title, $reset = FALSE) {
    *   - status: NODE_PUBLISHED.
    *   - sticky: NODE_NOT_STICKY.
    *   - type: 'page'.
-   *   - langcode: Language::LANGCODE_NOT_SPECIFIED.
+   *   - langcode: LanguageInterface::LANGCODE_NOT_SPECIFIED.
    *   - uid: The currently logged in user, or the user running test.
    *   - revision: 1. (Backwards-compatible binary flag indicating whether a
    *     new revision should be created; use 1 to specify a new revision.)
@@ -270,7 +270,7 @@ protected function drupalCreateNode(array $settings = array()) {
       'status'    => NODE_PUBLISHED,
       'sticky'    => NODE_NOT_STICKY,
       'type'      => 'page',
-      'langcode'  => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode'  => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     );
 
     // Use the original node's created time for existing nodes.
diff --git a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php
index 16c1fda..33910ab 100644
--- a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php
+++ b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\statistics\Tests;
 
-use Drupal\Core\Language\Language;
 
 /**
  * Tests statistics token replacement in strings.
@@ -56,7 +55,7 @@ function testStatisticsTokenReplacement() {
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = \Drupal::token()->replace($input, array('node' => $node), array('langcode' => $language_interface->id));
+      $output = \Drupal::token()->replace($input, array('node' => $node), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Statistics token %token replaced.', array('%token' => $input)));
     }
   }
diff --git a/core/modules/system/core.api.php b/core/modules/system/core.api.php
index f2cc90e..7060ca6 100644
--- a/core/modules/system/core.api.php
+++ b/core/modules/system/core.api.php
@@ -412,7 +412,7 @@
  *
  * Example:
  * @code
- * $cid = 'mymodule_example:' . \Drupal::languageManager()->getCurrentLanguage()->id();
+ * $cid = 'mymodule_example:' . \Drupal::languageManager()->getCurrentLanguage()->getId();
  *
  * $data = NULL;
  * if ($cache = \Drupal::cache()->get($cid)) {
diff --git a/core/modules/system/language.api.php b/core/modules/system/language.api.php
index ed6de6c..f90a1fe 100644
--- a/core/modules/system/language.api.php
+++ b/core/modules/system/language.api.php
@@ -27,8 +27,8 @@
 function hook_language_switch_links_alter(array &$links, $type, $path) {
   $language_interface = \Drupal::languageManager()->getCurrentLanguage();
 
-  if ($type == \Drupal\Core\Language\Language::TYPE_CONTENT && isset($links[$language_interface->id])) {
-    foreach ($links[$language_interface->id] as $link) {
+  if ($type == \Drupal\Core\Language\LanguageInterface::TYPE_CONTENT && isset($links[$language_interface->id])) {
+    foreach ($links[$language_interface->getId()] as $link) {
       $link['attributes']['class'][] = 'active-language';
     }
   }
diff --git a/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php b/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php
index 3dfb81e..0d7f8fb 100644
--- a/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php
+++ b/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Ajax\ReplaceCommand;
 use Drupal\Core\Config\Entity\ConfigEntityStorageInterface;
 use Drupal\Core\Datetime\Date;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Entity\EntityForm;
@@ -160,7 +160,7 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#type' => 'language_select',
       '#title' => t('Language'),
-      '#languages' => Language::STATE_ALL,
+      '#languages' => LanguageInterface::STATE_ALL,
       '#default_value' => $this->entity->langcode,
     );
 
diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/FormatDateTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/FormatDateTest.php
index 171b915..3ddbf14 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/FormatDateTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/FormatDateTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Common;
 
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -113,7 +114,7 @@ function testFormatDate() {
       'predefined_langcode' => 'custom',
       'langcode' => self::LANGCODE,
       'name' => self::LANGCODE,
-      'direction' => Language::DIRECTION_LTR,
+      'direction' => LanguageInterface::DIRECTION_LTR,
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
 
@@ -132,8 +133,8 @@ function testFormatDate() {
     // Save the original user and language and then replace it with the test user and language.
     $real_user = $user;
     $user = user_load($test_user->id(), TRUE);
-    $real_language = $language_interface->id;
-    $language_interface->id = $user->getPreferredLangcode();
+    $real_language = $language_interface->getId();
+    $language_interface->setId($user->getPreferredLangcode());
     // Simulate a Drupal bootstrap with the logged-in user.
     date_default_timezone_set(drupal_get_user_timezone());
 
@@ -155,7 +156,7 @@ function testFormatDate() {
 
     // Restore the original user and language, and enable session saving.
     $user = $real_user;
-    $language_interface->id = $real_language;
+    $language_interface->setId($real_language);
     // Restore default time zone.
     date_default_timezone_set(drupal_get_user_timezone());
     \Drupal::service('session_manager')->enable();
diff --git a/core/modules/system/lib/Drupal/system/Tests/Common/UrlTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/UrlTest.php
index 7cda6a3..d59492d 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Common/UrlTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/UrlTest.php
@@ -66,7 +66,7 @@ function testLinkAttributes() {
       '#href' => 'http://drupal.org',
       '#title' => 'bar',
     );
-    $langcode = $language->id;
+    $langcode = $language->getId();
 
     // Test that the default hreflang handling for links does not override a
     // hreflang attribute explicitly set in the render array.
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCrudHookTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCrudHookTest.php
index 1d49a02..0c19fff 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCrudHookTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityCrudHookTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\system\Tests\Entity;
 
 use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Database\Database;
 
 /**
@@ -148,7 +148,7 @@ public function testCommentHooks() {
       'status' => 1,
       'promote' => 0,
       'sticky' => 0,
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'created' => REQUEST_TIME,
       'changed' => REQUEST_TIME,
     ));
@@ -167,7 +167,7 @@ public function testCommentHooks() {
       'created' => REQUEST_TIME,
       'changed' => REQUEST_TIME,
       'status' => 1,
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
 
     $this->assertHookMessageOrder(array(
@@ -292,7 +292,7 @@ public function testNodeHooks() {
       'status' => 1,
       'promote' => 0,
       'sticky' => 0,
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'created' => REQUEST_TIME,
       'changed' => REQUEST_TIME,
     ));
@@ -351,7 +351,7 @@ public function testTaxonomyTermHooks() {
     $vocabulary = entity_create('taxonomy_vocabulary', array(
       'name' => 'Test vocabulary',
       'vid' => 'test',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'description' => NULL,
       'module' => 'entity_crud_hook_test',
     ));
@@ -361,7 +361,7 @@ public function testTaxonomyTermHooks() {
     $term = entity_create('taxonomy_term', array(
       'vid' => $vocabulary->id(),
       'name' => 'Test term',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'description' => NULL,
       'format' => 1,
     ));
@@ -420,7 +420,7 @@ public function testTaxonomyVocabularyHooks() {
     $vocabulary = entity_create('taxonomy_vocabulary', array(
       'name' => 'Test vocabulary',
       'vid' => 'test',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'description' => NULL,
       'module' => 'entity_crud_hook_test',
     ));
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldDefaultValueTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldDefaultValueTest.php
index d624080..8f7e23f 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldDefaultValueTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldDefaultValueTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\system\Tests\Entity;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Component\Uuid\Uuid;
 use Drupal\Component\Utility\String;
 
@@ -55,7 +55,7 @@ public function testDefaultValues() {
    */
   protected function assertDefaultValues($entity_type) {
     $entity = entity_create($entity_type);
-    $this->assertEqual($entity->langcode->value, Language::LANGCODE_NOT_SPECIFIED, String::format('%entity_type: Default language', array('%entity_type' => $entity_type)));
+    $this->assertEqual($entity->langcode->value, LanguageInterface::LANGCODE_NOT_SPECIFIED, String::format('%entity_type: Default language', array('%entity_type' => $entity_type)));
     $this->assertTrue(Uuid::isValid($entity->uuid->value), String::format('%entity_type: Default UUID', array('%entity_type' => $entity_type)));
     $this->assertEqual($entity->name->getValue(), array(0 => array('value' => NULL)), 'Field has one empty value by default.');
   }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
index a838d2f..f593dfc 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityFieldTest.php
@@ -12,7 +12,7 @@
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FieldItemInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\TypedData\ComplexDataDefinitionInterface;
 use Drupal\Core\TypedData\DataDefinitionInterface;
 use Drupal\Core\TypedData\Type\StringInterface;
@@ -190,18 +190,18 @@ protected function assertReadWrite($entity_type) {
     $this->assertFalse(isset($entity->name->value), format_string('%entity_type: Name is not set.', array('%entity_type' => $entity_type)));
 
     // Access the language field.
-    $this->assertEqual(Language::LANGCODE_NOT_SPECIFIED, $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
-    $this->assertEqual(\Drupal::languageManager()->getLanguage(Language::LANGCODE_NOT_SPECIFIED), $entity->langcode->language, format_string('%entity_type: Language object can be read.', array('%entity_type' => $entity_type)));
+    $this->assertEqual(LanguageInterface::LANGCODE_NOT_SPECIFIED, $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
+    $this->assertEqual(\Drupal::languageManager()->getLanguage(LanguageInterface::LANGCODE_NOT_SPECIFIED), $entity->langcode->language, format_string('%entity_type: Language object can be read.', array('%entity_type' => $entity_type)));
 
     // Change the language by code.
-    $entity->langcode->value = \Drupal::languageManager()->getDefaultLanguage()->id;
-    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->id, $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
+    $entity->langcode->value = \Drupal::languageManager()->getDefaultLanguage()->getId();
+    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->getId(), $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
     $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage(), $entity->langcode->language, format_string('%entity_type: Language object can be read.', array('%entity_type' => $entity_type)));
 
     // Revert language by code then try setting it by language object.
-    $entity->langcode->value = Language::LANGCODE_NOT_SPECIFIED;
+    $entity->langcode->value = LanguageInterface::LANGCODE_NOT_SPECIFIED;
     $entity->langcode->language = \Drupal::languageManager()->getDefaultLanguage();
-    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->id, $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
+    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->getId(), $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
     $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage(), $entity->langcode->language, format_string('%entity_type: Language object can be read.', array('%entity_type' => $entity_type)));
 
     // Access the text field and test updating.
@@ -329,8 +329,8 @@ protected function assertSave($entity_type) {
     // Access the name field.
     $this->assertEqual(1, $entity->id->value, format_string('%entity_type: ID value can be read.', array('%entity_type' => $entity_type)));
     $this->assertTrue(is_string($entity->uuid->value), format_string('%entity_type: UUID value can be read.', array('%entity_type' => $entity_type)));
-    $this->assertEqual(Language::LANGCODE_NOT_SPECIFIED, $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
-    $this->assertEqual(\Drupal::languageManager()->getLanguage(Language::LANGCODE_NOT_SPECIFIED), $entity->langcode->language, format_string('%entity_type: Language object can be read.', array('%entity_type' => $entity_type)));
+    $this->assertEqual(LanguageInterface::LANGCODE_NOT_SPECIFIED, $entity->langcode->value, format_string('%entity_type: Language code can be read.', array('%entity_type' => $entity_type)));
+    $this->assertEqual(\Drupal::languageManager()->getLanguage(LanguageInterface::LANGCODE_NOT_SPECIFIED), $entity->langcode->language, format_string('%entity_type: Language object can be read.', array('%entity_type' => $entity_type)));
     $this->assertEqual($this->entity_user->id(), $entity->user_id->target_id, format_string('%entity_type: User id can be read.', array('%entity_type' => $entity_type)));
     $this->assertEqual($this->entity_user->getUsername(), $entity->user_id->entity->name->value, format_string('%entity_type: User name can be read.', array('%entity_type' => $entity_type)));
     $this->assertEqual($this->entity_field_text, $entity->field_test_text->value, format_string('%entity_type: Text field can be read.', array('%entity_type' => $entity_type)));
@@ -504,7 +504,7 @@ protected function assertDataStructureInterfaces($entity_type) {
     // the user name and other user entity strings as well.
     $target_strings = array(
       $entity->uuid->value,
-      Language::LANGCODE_NOT_SPECIFIED,
+      LanguageInterface::LANGCODE_NOT_SPECIFIED,
       $this->entity_name,
       // Bundle name.
       $entity->bundle(),
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityLanguageTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityLanguageTestBase.php
index ada2fbd..91a6bae 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityLanguageTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityLanguageTestBase.php
@@ -106,7 +106,7 @@ function setUp() {
 
     // Create the default languages.
     $default_language = language_save($this->languageManager->getDefaultLanguage());
-    $languages = $this->languageManager->getDefaultLockedLanguages($default_language->weight);
+    $languages = $this->languageManager->getDefaultLockedLanguages($default_language->getWeight());
     foreach ($languages as $language) {
       language_save($language);
     }
@@ -119,7 +119,7 @@ function setUp() {
         'name' => $this->randomString(),
         'weight' => $i,
       ));
-      $this->langcodes[$i] = $language->id;
+      $this->langcodes[$i] = $language->getId();
       language_save($language);
     }
   }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationFormTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationFormTest.php
index 8c0288e..1d5c15b 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationFormTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationFormTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Entity;
 
 use Drupal\field\Entity\FieldConfig;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
 
@@ -45,7 +46,7 @@ function setUp() {
         'id' => 'l' . $i,
         'name' => $this->randomString(),
       ));
-      $this->langcodes[$i] = $language->id;
+      $this->langcodes[$i] = $language->getId();
       language_save($language);
     }
   }
@@ -59,7 +60,7 @@ function testEntityFormLanguage() {
     $web_user = $this->drupalCreateUser(array('create page content', 'edit own page content', 'administer content types'));
     $this->drupalLogin($web_user);
 
-    // Create a node with language Language::LANGCODE_NOT_SPECIFIED.
+    // Create a node with language LanguageInterface::LANGCODE_NOT_SPECIFIED.
     $edit = array();
     $edit['title[0][value]'] = $this->randomName(8);
     $edit['body[0][value]'] = $this->randomName(16);
@@ -69,12 +70,12 @@ function testEntityFormLanguage() {
     $this->drupalPostForm(NULL, $edit, t('Save'));
 
     $node = $this->drupalGetNodeByTitle($edit['title[0][value]']);
-    $this->assertTrue($node->language()->id == $form_langcode, 'Form language is the same as the entity language.');
+    $this->assertTrue($node->language()->getId() == $form_langcode, 'Form language is the same as the entity language.');
 
     // Edit the node and test the form language.
     $this->drupalGet($this->langcodes[0] . '/node/' . $node->id() . '/edit');
     $form_langcode = \Drupal::state()->get('entity_test.form_langcode') ?: FALSE;
-    $this->assertTrue($node->language()->id == $form_langcode, 'Form language is the same as the entity language.');
+    $this->assertTrue($node->language()->getId() == $form_langcode, 'Form language is the same as the entity language.');
 
     // Explicitly set form langcode.
     $langcode = $this->langcodes[0];
@@ -85,7 +86,7 @@ function testEntityFormLanguage() {
 
     // Enable language selector.
     $this->drupalGet('admin/structure/types/manage/page');
-    $edit = array('language_configuration[language_show]' => TRUE, 'language_configuration[langcode]' => Language::LANGCODE_NOT_SPECIFIED);
+    $edit = array('language_configuration[language_show]' => TRUE, 'language_configuration[langcode]' => LanguageInterface::LANGCODE_NOT_SPECIFIED);
     $this->drupalPostForm('admin/structure/types/manage/page', $edit, t('Save content type'));
     $this->assertRaw(t('The content type %type has been updated.', array('%type' => 'Basic page')), 'Basic page content type has been updated.');
 
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php
index 2086c14..1e5a08a 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityTranslationTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\system\Tests\Entity;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\entity_test\Entity\EntityTestMulRev;
 
 /**
@@ -44,15 +44,15 @@ protected function _testEntityLanguageMethods($entity_type) {
       'name' => 'test',
       'user_id' => $this->container->get('current_user')->id(),
     ));
-    $this->assertEqual($entity->language()->id, Language::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Entity language not specified.', array('%entity_type' => $entity_type)));
+    $this->assertEqual($entity->language()->getId(), LanguageInterface::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Entity language not specified.', array('%entity_type' => $entity_type)));
     $this->assertFalse($entity->getTranslationLanguages(FALSE), format_string('%entity_type: No translations are available', array('%entity_type' => $entity_type)));
 
     // Set the value in default language.
     $entity->set($this->field_name, array(0 => array('value' => 'default value')));
     // Get the value.
-    $field = $entity->getTranslation(Language::LANGCODE_DEFAULT)->get($this->field_name);
+    $field = $entity->getTranslation(LanguageInterface::LANGCODE_DEFAULT)->get($this->field_name);
     $this->assertEqual($field->value, 'default value', format_string('%entity_type: Untranslated value retrieved.', array('%entity_type' => $entity_type)));
-    $this->assertEqual($field->getLangcode(), Language::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Field object has the expected langcode.', array('%entity_type' => $entity_type)));
+    $this->assertEqual($field->getLangcode(), LanguageInterface::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Field object has the expected langcode.', array('%entity_type' => $entity_type)));
 
     // Set the value in a certain language. As the entity is not
     // language-specific it should use the default language and so ignore the
@@ -65,7 +65,7 @@ protected function _testEntityLanguageMethods($entity_type) {
     // language-specific entity.
     $field = $entity->getTranslation($this->langcodes[1])->get($this->field_name);
     $this->assertEqual($field->value, 'default value2', format_string('%entity_type: Untranslated value retrieved.', array('%entity_type' => $entity_type)));
-    $this->assertEqual($field->getLangcode(), Language::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Field object has the expected langcode.', array('%entity_type' => $entity_type)));
+    $this->assertEqual($field->getLangcode(), LanguageInterface::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Field object has the expected langcode.', array('%entity_type' => $entity_type)));
 
     // Now, make the entity language-specific by assigning a language and test
     // translating it.
@@ -152,12 +152,12 @@ protected function _testMultilingualProperties($entity_type) {
     $entity = entity_create($entity_type, array('name' => $name, 'user_id' => $uid));
     $entity->save();
     $entity = entity_load($entity_type, $entity->id());
-    $default_langcode = $entity->language()->id;
-    $this->assertEqual($default_langcode, Language::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Entity created as language neutral.', array('%entity_type' => $entity_type)));
-    $field = $entity->getTranslation(Language::LANGCODE_DEFAULT)->get('name');
+    $default_langcode = $entity->language()->getId();
+    $this->assertEqual($default_langcode, LanguageInterface::LANGCODE_NOT_SPECIFIED, format_string('%entity_type: Entity created as language neutral.', array('%entity_type' => $entity_type)));
+    $field = $entity->getTranslation(LanguageInterface::LANGCODE_DEFAULT)->get('name');
     $this->assertEqual($name, $field->value, format_string('%entity_type: The entity name has been correctly stored as language neutral.', array('%entity_type' => $entity_type)));
     $this->assertEqual($default_langcode, $field->getLangcode(), format_string('%entity_type: The field object has the expect langcode.', array('%entity_type' => $entity_type)));
-    $this->assertEqual($uid, $entity->getTranslation(Language::LANGCODE_DEFAULT)->get('user_id')->target_id, format_string('%entity_type: The entity author has been correctly stored as language neutral.', array('%entity_type' => $entity_type)));
+    $this->assertEqual($uid, $entity->getTranslation(LanguageInterface::LANGCODE_DEFAULT)->get('user_id')->target_id, format_string('%entity_type: The entity author has been correctly stored as language neutral.', array('%entity_type' => $entity_type)));
     $field = $entity->getTranslation($langcode)->get('name');
     $this->assertEqual($name, $field->value, format_string('%entity_type: The entity name defaults to neutral language.', array('%entity_type' => $entity_type)));
     $this->assertEqual($default_langcode, $field->getLangcode(), format_string('%entity_type: The field object has the expect langcode.', array('%entity_type' => $entity_type)));
@@ -172,18 +172,18 @@ protected function _testMultilingualProperties($entity_type) {
     $entity = entity_create($entity_type, array('name' => $name, 'user_id' => $uid, 'langcode' => $langcode));
     $entity->save();
     $entity = entity_load($entity_type, $entity->id());
-    $default_langcode = $entity->language()->id;
+    $default_langcode = $entity->language()->getId();
     $this->assertEqual($default_langcode, $langcode, format_string('%entity_type: Entity created as language specific.', array('%entity_type' => $entity_type)));
     $field = $entity->getTranslation($langcode)->get('name');
     $this->assertEqual($name, $field->value, format_string('%entity_type: The entity name has been correctly stored as a language-aware property.', array('%entity_type' => $entity_type)));
     $this->assertEqual($default_langcode, $field->getLangcode(), format_string('%entity_type: The field object has the expect langcode.', array('%entity_type' => $entity_type)));
     $this->assertEqual($uid, $entity->getTranslation($langcode)->get('user_id')->target_id, format_string('%entity_type: The entity author has been correctly stored as a language-aware property.', array('%entity_type' => $entity_type)));
     // Translatable properties on a translatable entity should use default
-    // language if Language::LANGCODE_NOT_SPECIFIED is passed.
-    $field = $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get('name');
+    // language if LanguageInterface::LANGCODE_NOT_SPECIFIED is passed.
+    $field = $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get('name');
     $this->assertEqual($name, $field->value, format_string('%entity_type: The entity name defaults to the default language.', array('%entity_type' => $entity_type)));
     $this->assertEqual($default_langcode, $field->getLangcode(), format_string('%entity_type: The field object has the expect langcode.', array('%entity_type' => $entity_type)));
-    $this->assertEqual($uid, $entity->getTranslation(Language::LANGCODE_NOT_SPECIFIED)->get('user_id')->target_id, format_string('%entity_type: The entity author defaults to the default language.', array('%entity_type' => $entity_type)));
+    $this->assertEqual($uid, $entity->getTranslation(LanguageInterface::LANGCODE_NOT_SPECIFIED)->get('user_id')->target_id, format_string('%entity_type: The entity author defaults to the default language.', array('%entity_type' => $entity_type)));
     $field = $entity->get('name');
     $this->assertEqual($name, $field->value, format_string('%entity_type: The entity name can be retrieved without specifying a language.', array('%entity_type' => $entity_type)));
     $this->assertEqual($default_langcode, $field->getLangcode(), format_string('%entity_type: The field object has the expect langcode.', array('%entity_type' => $entity_type)));
@@ -221,7 +221,7 @@ protected function _testMultilingualProperties($entity_type) {
       );
       $field = $entity->getTranslation($langcode)->get('name');
       $this->assertEqual($properties[$langcode]['name'][0], $field->value, format_string('%entity_type: The entity name has been correctly stored for language %langcode.', $args));
-      $field_langcode = ($langcode == $entity->language()->id) ? $default_langcode : $langcode;
+      $field_langcode = ($langcode == $entity->language()->getId()) ? $default_langcode : $langcode;
       $this->assertEqual($field_langcode, $field->getLangcode(), format_string('%entity_type: The field object has the expected langcode  %langcode.', $args));
       $this->assertEqual($properties[$langcode]['user_id'][0], $entity->getTranslation($langcode)->get('user_id')->target_id, format_string('%entity_type: The entity author has been correctly stored for language %langcode.', $args));
     }
@@ -309,7 +309,7 @@ function testEntityTranslationAPI() {
     $entity->langcode->value = $default_langcode;
     $translation = $entity->getTranslation($default_langcode);
     $this->assertEqual($entity, $translation, 'The translation object corresponding to the default language (explicit) is the entity object itself.');
-    $translation = $entity->getTranslation(Language::LANGCODE_DEFAULT);
+    $translation = $entity->getTranslation(LanguageInterface::LANGCODE_DEFAULT);
     $this->assertEqual($entity, $translation, 'The translation object corresponding to the default language (implicit) is the entity object itself.');
 
     // Create a translation and verify that the translation object and the
@@ -320,8 +320,8 @@ function testEntityTranslationAPI() {
     $translation = $entity->addTranslation($langcode);
     $this->assertNotIdentical($entity, $translation, 'The entity and the translation object differ from one another.');
     $this->assertTrue($entity->hasTranslation($langcode), 'The new translation exists.');
-    $this->assertEqual($translation->language()->id, $langcode, 'The translation language matches the specified one.');
-    $this->assertEqual($translation->getUntranslated()->language()->id, $default_langcode, 'The original language can still be retrieved.');
+    $this->assertEqual($translation->language()->getId(), $langcode, 'The translation language matches the specified one.');
+    $this->assertEqual($translation->getUntranslated()->language()->getId(), $default_langcode, 'The original language can still be retrieved.');
     $translation->name->value = $name_translated;
     $this->assertEqual($entity->name->value, $name, 'The original name is retained after setting a translated value.');
     $entity->name->value = $name;
@@ -335,16 +335,16 @@ function testEntityTranslationAPI() {
 
     // Check that after loading an entity the language is the default one.
     $entity = $this->reloadEntity($entity);
-    $this->assertEqual($entity->language()->id, $default_langcode, 'The loaded entity is the original one.');
+    $this->assertEqual($entity->language()->getId(), $default_langcode, 'The loaded entity is the original one.');
 
     // Add another translation and check that everything works as expected. A
     // new translation object can be obtained also by just specifying a valid
     // language.
     $langcode2 = $this->langcodes[2];
     $translation = $entity->getTranslation($langcode2);
-    $value = $entity !== $translation && $translation->language()->id == $langcode2 && $entity->hasTranslation($langcode2);
+    $value = $entity !== $translation && $translation->language()->getId() == $langcode2 && $entity->hasTranslation($langcode2);
     $this->assertTrue($value, 'A new translation object can be obtained also by specifying a valid language.');
-    $this->assertEqual($entity->language()->id, $default_langcode, 'The original language has been preserved.');
+    $this->assertEqual($entity->language()->getId(), $default_langcode, 'The original language has been preserved.');
     $translation->save();
     $hooks = $this->getHooksInfo();
     $this->assertEqual($hooks['entity_translation_insert'], $langcode2, 'The generic entity translation insertion hook has fired.');
@@ -377,7 +377,7 @@ function testEntityTranslationAPI() {
 
     // Check that removing an invalid translation causes an exception to be
     // thrown.
-    foreach (array($default_langcode, Language::LANGCODE_DEFAULT, $this->randomName()) as $invalid_langcode) {
+    foreach (array($default_langcode, LanguageInterface::LANGCODE_DEFAULT, $this->randomName()) as $invalid_langcode) {
       $message = format_string('Removing an invalid translation (@langcode) causes an exception to be thrown.', array('@langcode' => $invalid_langcode));
       try {
         $entity->removeTranslation($invalid_langcode);
@@ -448,7 +448,7 @@ function testEntityTranslationAPI() {
    * Tests language fallback applied to field and entity translations.
    */
   function testLanguageFallback() {
-    $current_langcode = $this->languageManager->getCurrentLanguage(Language::TYPE_CONTENT)->id;
+    $current_langcode = $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();
     $this->langcodes[] = $current_langcode;
 
     $values = array();
@@ -472,21 +472,21 @@ function testLanguageFallback() {
     // Check that retrieveing the current translation works as expected.
     $entity = $this->reloadEntity($entity);
     $translation = $this->entityManager->getTranslationFromContext($entity, $langcode2);
-    $this->assertEqual($translation->language()->id, $default_langcode, 'The current translation language matches the expected one.');
+    $this->assertEqual($translation->language()->getId(), $default_langcode, 'The current translation language matches the expected one.');
 
     // Check that language fallback respects language weight by default.
     $languages = $this->languageManager->getLanguages();
-    $languages[$langcode]->weight = -1;
+    $languages[$langcode]->setWeight(-1);
     language_save($languages[$langcode]);
     $translation = $this->entityManager->getTranslationFromContext($entity, $langcode2);
-    $this->assertEqual($translation->language()->id, $langcode, 'The current translation language matches the expected one.');
+    $this->assertEqual($translation->language()->getId(), $langcode, 'The current translation language matches the expected one.');
 
     // Check that the current translation is properly returned.
     $translation = $this->entityManager->getTranslationFromContext($entity);
-    $this->assertEqual($langcode, $translation->language()->id, 'The current translation language matches the topmost language fallback candidate.');
+    $this->assertEqual($langcode, $translation->language()->getId(), 'The current translation language matches the topmost language fallback candidate.');
     $entity->addTranslation($current_langcode, $values[$current_langcode]);
     $translation = $this->entityManager->getTranslationFromContext($entity);
-    $this->assertEqual($current_langcode, $translation->language()->id, 'The current translation language matches the current language.');
+    $this->assertEqual($current_langcode, $translation->language()->getId(), 'The current translation language matches the current language.');
 
     // Check that if the entity has no translation no fallback is applied.
     $entity2 = $controller->create(array('langcode' => $default_langcode));
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/FieldSqlStorageTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/FieldSqlStorageTest.php
index 8549d99..866cc9c 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/FieldSqlStorageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/FieldSqlStorageTest.php
@@ -117,13 +117,13 @@ function testFieldLoad() {
       for ($delta = 0; $delta <= $this->field_cardinality; $delta++) {
         $value = mt_rand(1, 127);
         $values[$revision_id][] = $value;
-        $query->values(array($bundle, 0, $entity->id(), $revision_id, $delta, $entity->language()->id, $value));
+        $query->values(array($bundle, 0, $entity->id(), $revision_id, $delta, $entity->language()->getId(), $value));
       }
       $query->execute();
     }
     $query = db_insert($this->table)->fields($columns);
     foreach ($values[$revision_id] as $delta => $value) {
-      $query->values(array($bundle, 0, $entity->id(), $revision_id, $delta, $entity->language()->id, $value));
+      $query->values(array($bundle, 0, $entity->id(), $revision_id, $delta, $entity->language()->getId(), $value));
     }
     $query->execute();
 
@@ -187,7 +187,7 @@ function testFieldWrite() {
         'deleted' => 0,
         'entity_id' => $entity->id(),
         'revision_id' => $entity->getRevisionId(),
-        'langcode' => $entity->language()->id,
+        'langcode' => $entity->language()->getId(),
         'delta' => $delta,
         $this->field_name . '_value' => $values[$delta]['value'],
       );
@@ -210,7 +210,7 @@ function testFieldWrite() {
         'deleted' => 0,
         'entity_id' => $entity->id(),
         'revision_id' => $entity->getRevisionId(),
-        'langcode' => $entity->language()->id,
+        'langcode' => $entity->language()->getId(),
         'delta' => $delta,
         $this->field_name . '_value' => $values[$delta]['value'],
       );
@@ -238,7 +238,7 @@ function testFieldWrite() {
           'deleted' => 0,
           'entity_id' => $entity->id(),
           'revision_id' => $revision_id,
-          'langcode' => $entity->language()->id,
+          'langcode' => $entity->language()->getId(),
           'delta' => $delta,
           $this->field_name . '_value' => $values[$delta]['value'],
         );
diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/FieldTranslationSqlStorageTest.php b/core/modules/system/lib/Drupal/system/Tests/Entity/FieldTranslationSqlStorageTest.php
index b9d8cec..ec3425a 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/FieldTranslationSqlStorageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/FieldTranslationSqlStorageTest.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Entity\ContentEntityDatabaseStorage;
 use Drupal\Core\Language\Language;
 use Drupal\field\Entity\FieldConfig;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests entity translation.
@@ -48,7 +49,7 @@ public function testFieldSqlStorage() {
     $entity->langcode->value = $langcode;
     $entity->save();
     $this->assertFieldStorageLangcode($entity, 'Field language successfully changed.');
-    $langcode = Language::LANGCODE_NOT_SPECIFIED;
+    $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
     $entity->langcode->value = $langcode;
     $entity->save();
     $this->assertFieldStorageLangcode($entity, 'Field language successfully changed to language neutral.');
@@ -87,7 +88,7 @@ protected function assertFieldStorageLangcode(ContentEntityInterface $entity, $m
     $status = TRUE;
     $entity_type = $entity->getEntityTypeId();
     $id = $entity->id();
-    $langcode = $entity->getUntranslated()->language()->id;
+    $langcode = $entity->getUntranslated()->language()->getId();
     $fields = array($this->field_name, $this->untranslatable_field_name);
 
     foreach ($fields as $field_name) {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Form/LanguageSelectElementTest.php b/core/modules/system/lib/Drupal/system/Tests/Form/LanguageSelectElementTest.php
index f501ad1..991cdde 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Form/LanguageSelectElementTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Form/LanguageSelectElementTest.php
@@ -10,6 +10,7 @@
 use Drupal\Component\Serialization\Json;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Functional tests for the language select form element.
@@ -52,15 +53,15 @@ function testLanguageSelectElementOptions() {
 
     $this->drupalGet('form-test/language_select');
     // Check that the language fields were rendered on the page.
-    $ids = array('edit-languages-all' => Language::STATE_ALL,
-                 'edit-languages-configurable' => Language::STATE_CONFIGURABLE,
-                 'edit-languages-locked' => Language::STATE_LOCKED,
-                 'edit-languages-config-and-locked' => Language::STATE_CONFIGURABLE | Language::STATE_LOCKED);
+    $ids = array('edit-languages-all' => LanguageInterface::STATE_ALL,
+                 'edit-languages-configurable' => LanguageInterface::STATE_CONFIGURABLE,
+                 'edit-languages-locked' => LanguageInterface::STATE_LOCKED,
+                 'edit-languages-config-and-locked' => LanguageInterface::STATE_CONFIGURABLE | LanguageInterface::STATE_LOCKED);
     foreach ($ids as $id => $flags) {
       $this->assertField($id, format_string('The @id field was found on the page.', array('@id' => $id)));
       $options = array();
       foreach ($this->container->get('language_manager')->getLanguages($flags) as $langcode => $language) {
-        $options[$langcode] = $language->locked ? t('- @name -', array('@name' => $language->name)) : $language->name;
+        $options[$langcode] = $language->isLocked() ? t('- @name -', array('@name' => $language->getName())) : $language->getName();
       }
       $this->_testLanguageSelectElementOptions($id, $options);
     }
@@ -93,7 +94,7 @@ function testHiddenLanguageSelectElement() {
     $values = Json::decode($this->drupalGetContent());
     $this->assertEqual($values['languages_all'], 'xx');
     $this->assertEqual($values['languages_configurable'], 'en');
-    $this->assertEqual($values['languages_locked'], Language::LANGCODE_NOT_SPECIFIED);
+    $this->assertEqual($values['languages_locked'], LanguageInterface::LANGCODE_NOT_SPECIFIED);
     $this->assertEqual($values['languages_config_and_locked'], 'dummy_value');
     $this->assertEqual($values['language_custom_options'], 'opt2');
   }
diff --git a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueContentEntityStorageTest.php b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueContentEntityStorageTest.php
index 10aec9b..5930939 100644
--- a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueContentEntityStorageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/KeyValueContentEntityStorageTest.php
@@ -38,7 +38,7 @@ public static function getInfo() {
    * Tests CRUD operations.
    */
   function testCRUD() {
-    $default_langcode = language_default()->id;
+    $default_langcode = language_default()->getId();
     // Verify default properties on a newly created empty entity.
     $empty = entity_create('entity_test_label');
     $this->assertIdentical($empty->id->value, NULL);
diff --git a/core/modules/system/lib/Drupal/system/Tests/Mail/MailTest.php b/core/modules/system/lib/Drupal/system/Tests/Mail/MailTest.php
index 56aef7f..22443f2 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Mail/MailTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Mail/MailTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\system\Tests\Mail;
 
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -67,7 +66,7 @@ public function testCancelMessage() {
     \Drupal::state()->set('system.test_mail_collector', array());
 
     // Send a test message that simpletest_mail_alter should cancel.
-    drupal_mail('simpletest', 'cancel_test', 'cancel@example.com', $language_interface->id);
+    drupal_mail('simpletest', 'cancel_test', 'cancel@example.com', $language_interface->getId());
     // Retrieve sent message.
     $captured_emails = \Drupal::state()->get('system.test_mail_collector');
     $sent_message = end($captured_emails);
diff --git a/core/modules/system/lib/Drupal/system/Tests/Path/AliasTest.php b/core/modules/system/lib/Drupal/system/Tests/Path/AliasTest.php
index 0baae45..0c1b49b 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Path/AliasTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Path/AliasTest.php
@@ -154,7 +154,7 @@ function testLookupPath() {
     $aliasStorage->save('user/2', 'bar');
     // Hook that clears cache is not executed with unit tests.
     $aliasManager->cacheClear();
-    $this->assertEqual($aliasManager->getPathByAlias('bar'), 'user/2', 'Newer alias record is returned when comparing two Language::LANGCODE_NOT_SPECIFIED paths with the same alias.');
+    $this->assertEqual($aliasManager->getPathByAlias('bar'), 'user/2', 'Newer alias record is returned when comparing two LanguageInterface::LANGCODE_NOT_SPECIFIED paths with the same alias.');
   }
 
   /**
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/DateTimeTest.php b/core/modules/system/lib/Drupal/system/Tests/System/DateTimeTest.php
index 8f69047..cdb7ead 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/DateTimeTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/DateTimeTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\system\Tests\System;
 
 use Drupal\simpletest\WebTestBase;
-use Drupal\Core\Language\Language;
 
 /**
  * Tests generic date and time handling capabilities of Drupal.
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTest.php b/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTest.php
index 623d995..fefc8d7 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTest.php
@@ -45,7 +45,7 @@ public function testSystemTokenRecognition() {
     foreach ($tests as $test) {
       $input = $test['prefix'] . '[site:name]' . $test['suffix'];
       $expected = $test['prefix'] . 'Drupal' . $test['suffix'];
-      $output = $this->tokenService->replace($input, array(), array('langcode' => $this->languageInterface->id));
+      $output = $this->tokenService->replace($input, array(), array('langcode' => $this->languageInterface->getId()));
       $this->assertTrue($output == $expected, format_string('Token recognized in string %string', array('%string' => $input)));
     }
 
@@ -66,12 +66,12 @@ public function testClear() {
 
     // Replace with with the clear parameter, only the valid token should remain.
     $target = String::checkPlain(\Drupal::config('system.site')->get('name'));
-    $result = $this->tokenService->replace($source, array(), array('langcode' => $this->languageInterface->id, 'clear' => TRUE));
+    $result = $this->tokenService->replace($source, array(), array('langcode' => $this->languageInterface->getId(), 'clear' => TRUE));
     $this->assertEqual($target, $result, 'Valid tokens replaced while invalid tokens ignored.');
 
     $target .= '[user:name]';
     $target .= '[bogus:token]';
-    $result = $this->tokenService->replace($source, array(), array('langcode' => $this->languageInterface->id));
+    $result = $this->tokenService->replace($source, array(), array('langcode' => $this->languageInterface->getId()));
     $this->assertEqual($target, $result, 'Valid tokens replaced while invalid tokens ignored.');
   }
 
@@ -111,7 +111,7 @@ public function testSystemSiteTokenReplacement() {
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = $this->tokenService->replace($input, array(), array('langcode' => $this->languageInterface->id));
+      $output = $this->tokenService->replace($input, array(), array('langcode' => $this->languageInterface->getId()));
       $this->assertEqual($output, $expected, format_string('Sanitized system site information token %token replaced.', array('%token' => $input)));
     }
 
@@ -120,7 +120,7 @@ public function testSystemSiteTokenReplacement() {
     $tests['[site:slogan]'] = $config->get('slogan');
 
     foreach ($tests as $input => $expected) {
-      $output = $this->tokenService->replace($input, array(), array('langcode' => $this->languageInterface->id, 'sanitize' => FALSE));
+      $output = $this->tokenService->replace($input, array(), array('langcode' => $this->languageInterface->getId(), 'sanitize' => FALSE));
       $this->assertEqual($output, $expected, format_string('Unsanitized system site information token %token replaced.', array('%token' => $input)));
     }
 
@@ -146,18 +146,18 @@ public function testSystemDateTokenReplacement() {
     // Generate and test tokens.
     $tests = array();
     $date_service = \Drupal::service('date');
-    $tests['[date:short]'] = $date_service->format($date, 'short', '', NULL, $this->languageInterface->id);
-    $tests['[date:medium]'] = $date_service->format($date, 'medium', '', NULL, $this->languageInterface->id);
-    $tests['[date:long]'] = $date_service->format($date, 'long', '', NULL, $this->languageInterface->id);
-    $tests['[date:custom:m/j/Y]'] = $date_service->format($date, 'custom', 'm/j/Y', NULL, $this->languageInterface->id);
-    $tests['[date:since]'] = $date_service->formatInterval(REQUEST_TIME - $date, 2, $this->languageInterface->id);
+    $tests['[date:short]'] = $date_service->format($date, 'short', '', NULL, $this->languageInterface->getId());
+    $tests['[date:medium]'] = $date_service->format($date, 'medium', '', NULL, $this->languageInterface->getId());
+    $tests['[date:long]'] = $date_service->format($date, 'long', '', NULL, $this->languageInterface->getId());
+    $tests['[date:custom:m/j/Y]'] = $date_service->format($date, 'custom', 'm/j/Y', NULL, $this->languageInterface->getId());
+    $tests['[date:since]'] = $date_service->formatInterval(REQUEST_TIME - $date, 2, $this->languageInterface->getId());
     $tests['[date:raw]'] = Xss::filter($date);
 
     // Test to make sure that we generated something for each token.
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = $this->tokenService->replace($input, array('date' => $date), array('langcode' => $this->languageInterface->id));
+      $output = $this->tokenService->replace($input, array('date' => $date), array('langcode' => $this->languageInterface->getId()));
       $this->assertEqual($output, $expected, format_string('Date token %token replaced.', array('%token' => $input)));
     }
   }
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php b/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php
index c13bd4c..14602ad 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/TokenReplaceUnitTestBase.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\system\Tests\System;
 
-use Drupal\Core\Language\Language;
 use Drupal\system\Tests\Entity\EntityUnitTestBase;
 
 /**
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php b/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php
index 47d4557..7e8f3c6 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php
@@ -81,12 +81,12 @@ protected function setUp() {
 
     // Assign Lolspeak (xx) to be the default language.
     $language = \Drupal::languageManager()->getLanguage('xx');
-    $language->default = TRUE;
+    $language->setDefault(TRUE);
     language_save($language);
     $this->rebuildContainer();
 
     // Check that lolspeak is the default language for the site.
-    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->id, 'xx', 'Lolspeak is the default language');
+    $this->assertEqual(\Drupal::languageManager()->getDefaultLanguage()->getId(), 'xx', 'Lolspeak is the default language');
   }
 
   /**
diff --git a/core/modules/system/system.api.php b/core/modules/system/system.api.php
index c69838a..4011b9f 100644
--- a/core/modules/system/system.api.php
+++ b/core/modules/system/system.api.php
@@ -307,7 +307,7 @@ function hook_library_alter(array &$library, $name) {
 
     $language_interface = \Drupal::languageManager()->getCurrentLanguage();
     $settings['jquery']['ui']['datepicker'] = array(
-      'isRTL' => $language_interface->direction == Language::DIRECTION_RTL,
+      'isRTL' => $language_interface->getDirection() == LanguageInterface::DIRECTION_RTL,
       'firstDay' => \Drupal::config('system.date')->get('first_day'),
     );
     $library['js'][] = array(
@@ -1265,7 +1265,7 @@ function hook_watchdog(array $log_entry) {
     '@message'       => strip_tags($log_entry['message']),
   ));
 
-  drupal_mail('emaillog', 'entry', $to, $language_interface->id, $params);
+  drupal_mail('emaillog', 'entry', $to, $language_interface->getId(), $params);
 }
 
 /**
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index a14cd7b..74dbb8c 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -7,7 +7,6 @@
 
 use Drupal\Component\Utility\Crypt;
 use Drupal\Core\Database\Database;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\StreamWrapper\PublicStream;
 
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 8feb47b..aad2230 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -6,7 +6,7 @@
  */
 
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Extension\Extension;
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\block\BlockPluginInterface;
@@ -513,7 +513,7 @@ function system_element_info() {
   );
   $types['language_select'] = array(
     '#input' => TRUE,
-    '#default_value' => Language::LANGCODE_NOT_SPECIFIED,
+    '#default_value' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
   );
   $types['weight'] = array(
     '#input' => TRUE,
@@ -973,7 +973,7 @@ function system_page_build(&$page) {
       array(
         'path' => current_path(),
         'front' => drupal_is_front_page(),
-        'language' => \Drupal::languageManager()->getCurrentLanguage(\Drupal\Core\Language\Language::TYPE_URL)->id,
+        'language' => \Drupal::languageManager()->getCurrentLanguage(\Drupal\Core\Language\LanguageInterface::TYPE_URL)->getId(),
         'query' => \Drupal::service('request')->query->all(),
       )
     );
diff --git a/core/modules/system/tests/modules/entity_test/entity_test.module b/core/modules/system/tests/modules/entity_test/entity_test.module
index 9bc9682..2777dd9 100644
--- a/core/modules/system/tests/modules/entity_test/entity_test.module
+++ b/core/modules/system/tests/modules/entity_test/entity_test.module
@@ -392,28 +392,28 @@ function entity_test_entity_operation_alter(array &$operations, EntityInterface
  * Implements hook_entity_translation_insert().
  */
 function entity_test_entity_translation_insert(EntityInterface $translation) {
-  _entity_test_record_hooks('entity_translation_insert', $translation->language()->id);
+  _entity_test_record_hooks('entity_translation_insert', $translation->language()->getId());
 }
 
 /**
  * Implements hook_entity_translation_delete().
  */
 function entity_test_entity_translation_delete(EntityInterface $translation) {
-  _entity_test_record_hooks('entity_translation_delete', $translation->language()->id);
+  _entity_test_record_hooks('entity_translation_delete', $translation->language()->getId());
 }
 
 /**
  * Implements hook_ENTITY_TYPE_translation_insert().
  */
 function entity_test_entity_test_mul_translation_insert(EntityInterface $translation) {
-  _entity_test_record_hooks('entity_test_mul_translation_insert', $translation->language()->id);
+  _entity_test_record_hooks('entity_test_mul_translation_insert', $translation->language()->getId());
 }
 
 /**
  * Implements hook_ENTITY_TYPE_translation_delete().
  */
 function entity_test_entity_test_mul_translation_delete(EntityInterface $translation) {
-  _entity_test_record_hooks('entity_test_mul_translation_delete', $translation->language()->id);
+  _entity_test_record_hooks('entity_test_mul_translation_delete', $translation->language()->getId());
 }
 
 /**
diff --git a/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestAccessController.php b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestAccessController.php
index 034caa3..5f23487 100644
--- a/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestAccessController.php
+++ b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestAccessController.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityAccessController;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 
 /**
@@ -22,7 +22,7 @@ class EntityTestAccessController extends EntityAccessController {
    */
   protected function checkAccess(EntityInterface $entity, $operation, $langcode, AccountInterface $account) {
     if ($operation === 'view') {
-      if ($langcode != Language::LANGCODE_DEFAULT) {
+      if ($langcode != LanguageInterface::LANGCODE_DEFAULT) {
         return user_access('view test entity translations', $account);
       }
       return user_access('view test entity', $account);
diff --git a/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestForm.php b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestForm.php
index 849ea17..5aa5bde 100644
--- a/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestForm.php
+++ b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/EntityTestForm.php
@@ -7,7 +7,7 @@
 namespace Drupal\entity_test;
 
 use Drupal\Core\Entity\ContentEntityForm;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Form controller for the test entity edit forms.
@@ -44,8 +44,8 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#title' => t('Language'),
       '#type' => 'language_select',
-      '#default_value' => $entity->getUntranslated()->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#default_value' => $entity->getUntranslated()->language()->getId(),
+      '#languages' => LanguageInterface::STATE_ALL,
     );
 
     // @todo: Is there a better way to check if an entity type is revisionable?
diff --git a/core/modules/system/tests/modules/form_test/form_test.module b/core/modules/system/tests/modules/form_test/form_test.module
index 42ef667..38f5176 100644
--- a/core/modules/system/tests/modules/form_test/form_test.module
+++ b/core/modules/system/tests/modules/form_test/form_test.module
@@ -7,7 +7,7 @@
 
 use Drupal\Component\Serialization\Json;
 use Drupal\Core\Database\Database;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\form_test\Callbacks;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Symfony\Component\HttpFoundation\JsonResponse;
@@ -1000,30 +1000,30 @@ function form_test_language_select() {
   $form['languages_all'] = array(
     '#title' => t('Languages: All'),
     '#type' => 'language_select',
-    '#languages' => Language::STATE_ALL,
+    '#languages' => LanguageInterface::STATE_ALL,
     '#default_value' => 'xx',
   );
   $form['languages_configurable'] = array(
     '#title' => t('Languages: Configurable'),
     '#type' => 'language_select',
-    '#languages' => Language::STATE_CONFIGURABLE,
+    '#languages' => LanguageInterface::STATE_CONFIGURABLE,
     '#default_value' => 'en',
   );
   $form['languages_locked'] = array(
     '#title' => t('Languages: Locked'),
     '#type' => 'language_select',
-    '#languages' => Language::STATE_LOCKED,
+    '#languages' => LanguageInterface::STATE_LOCKED,
   );
   $form['languages_config_and_locked'] = array(
     '#title' => t('Languages: Configurable and locked'),
     '#type' => 'language_select',
-    '#languages' => Language::STATE_CONFIGURABLE | Language::STATE_LOCKED,
+    '#languages' => LanguageInterface::STATE_CONFIGURABLE | LanguageInterface::STATE_LOCKED,
     '#default_value' => 'dummy_value',
   );
   $form['language_custom_options'] = array(
     '#title' => t('Languages: Custom'),
     '#type' => 'language_select',
-    '#languages' => Language::STATE_CONFIGURABLE | Language::STATE_LOCKED,
+    '#languages' => LanguageInterface::STATE_CONFIGURABLE | LanguageInterface::STATE_LOCKED,
     '#options' => array('opt1' => 'First option', 'opt2' => 'Second option', 'opt3' => 'Third option'),
     '#default_value' => 'opt2',
   );
diff --git a/core/modules/system/tests/modules/form_test/lib/Drupal/form_test/Controller/FormTestController.php b/core/modules/system/tests/modules/form_test/lib/Drupal/form_test/Controller/FormTestController.php
index ad96815..600b1d9 100644
--- a/core/modules/system/tests/modules/form_test/lib/Drupal/form_test/Controller/FormTestController.php
+++ b/core/modules/system/tests/modules/form_test/lib/Drupal/form_test/Controller/FormTestController.php
@@ -7,7 +7,7 @@
 namespace Drupal\form_test\Controller;
 
 use Drupal\Core\Controller\ControllerBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Controller routines for form_test routes.
@@ -26,7 +26,7 @@ public function twoFormInstances() {
       'uid' => $user->id(),
       'name' => $user->getUsername(),
       'type' => 'page',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     );
     $node1 = $this->entityManager()->getStorage('node')->create($values);
     $node2 = clone($node1);
diff --git a/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/CachedMockBlockManager.php b/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/CachedMockBlockManager.php
index df79b31..b1bb1d8 100644
--- a/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/CachedMockBlockManager.php
+++ b/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/CachedMockBlockManager.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\plugin_test\Plugin;
 
-use Drupal\Core\Language\Language;
 use Drupal\Core\Plugin\Discovery\CacheDecorator;
 
 /**
@@ -25,6 +24,6 @@ public function __construct() {
     // The CacheDecorator allows us to cache these plugin definitions for
     // quicker retrieval. In this case we are generating a cache key by
     // language.
-    $this->discovery = new CacheDecorator($this->discovery, 'mock_block:' . \Drupal::languageManager()->getCurrentLanguage()->id, 'default',  1542646800, array('plugin_test'));
+    $this->discovery = new CacheDecorator($this->discovery, 'mock_block:' . \Drupal::languageManager()->getCurrentLanguage()->getId(), 'default',  1542646800, array('plugin_test'));
   }
 }
diff --git a/core/modules/system/tests/upgrade/drupal-7.language.database.php b/core/modules/system/tests/upgrade/drupal-7.language.database.php
index 8025354..95b80d2 100644
--- a/core/modules/system/tests/upgrade/drupal-7.language.database.php
+++ b/core/modules/system/tests/upgrade/drupal-7.language.database.php
@@ -422,7 +422,7 @@
 
 // Add sample nodes to test language assignment and translation functionality.
 // The first node is also used for testing comment language functionality. This
-// is a simple node with Language::LANGCODE_NOT_SPECIFIED as language code. The second
+// is a simple node with LanguageInterface::LANGCODE_NOT_SPECIFIED as language code. The second
 // node is a Catalan node (language code 'ca'). The third and fourth node are a
 // translation set with an English source translation (language code 'en') and
 // a Chuvash translation (language code 'cv').
@@ -545,7 +545,7 @@
   'vid' => '70',
   'uid' => '6',
   'title' => 'Node title 50',
-  'log' => 'Added a Language::LANGCODE_NOT_SPECIFIED node to comment on.',
+  'log' => 'Added a LanguageInterface::LANGCODE_NOT_SPECIFIED node to comment on.',
   'timestamp' => '1314997642',
   'status' => '1',
   'comment' => '2',
diff --git a/core/modules/system/theme.api.php b/core/modules/system/theme.api.php
index 50fa74e..8d121f6 100644
--- a/core/modules/system/theme.api.php
+++ b/core/modules/system/theme.api.php
@@ -288,7 +288,7 @@ function hook_theme_suggestions_HOOK(array $variables) {
  */
 function hook_theme_suggestions_alter(array &$suggestions, array $variables, $hook) {
   // Add an interface-language specific suggestion to all theme hooks.
-  $suggestions[] = $hook . '__' . \Drupal::languageManager()->getCurrentLanguage()->id;
+  $suggestions[] = $hook . '__' . \Drupal::languageManager()->getCurrentLanguage()->getId();
 }
 
 /**
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php
index 510524a..4e1f1f8 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Entity/Term.php
@@ -11,7 +11,6 @@
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Field\FieldDefinition;
-use Drupal\Core\Language\Language;
 use Drupal\Core\TypedData\DataDefinition;
 use Drupal\taxonomy\TermInterface;
 
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/views/field/Language.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/views/field/Language.php
index 13e3d23..6345f5b 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/views/field/Language.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Plugin/views/field/Language.php
@@ -22,7 +22,7 @@ class Language extends Taxonomy {
   public function render(ResultRow $values) {
     $value = $this->getValue($values);
     $language = language_load($value);
-    $value = $language ? $language->name : '';
+    $value = $language ? $language->getName() : '';
 
     return $this->renderLink($this->sanitizeValue($value), $values);
   }
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/TermForm.php b/core/modules/taxonomy/lib/Drupal/taxonomy/TermForm.php
index e3b048a..cfef112 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/TermForm.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/TermForm.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\ContentEntityForm;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Base for controller for taxonomy term edit forms.
@@ -32,8 +32,8 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#type' => 'language_select',
       '#title' => $this->t('Language'),
-      '#languages' => Language::STATE_ALL,
-      '#default_value' => $term->getUntranslated()->language()->id,
+      '#languages' => LanguageInterface::STATE_ALL,
+      '#default_value' => $term->getUntranslated()->language()->getId(),
       '#access' => !empty($language_configuration['language_show']),
     );
 
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php
index 0a67140..61be0d0 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTermReferenceItemTest.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FieldItemInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\field\Tests\FieldUnitTestBase;
 
 /**
@@ -48,7 +48,7 @@ public function setUp() {
     $vocabulary = entity_create('taxonomy_vocabulary', array(
       'name' => $this->randomName(),
       'vid' => drupal_strtolower($this->randomName()),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $vocabulary->save();
 
@@ -74,7 +74,7 @@ public function setUp() {
     $this->term = entity_create('taxonomy_term', array(
       'name' => $this->randomName(),
       'vid' => $vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $this->term->save();
   }
@@ -110,7 +110,7 @@ public function testTaxonomyTermReferenceItem() {
     $term2 = entity_create('taxonomy_term', array(
       'name' => $this->randomName(),
       'vid' => $this->term->getVocabularyId(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term2->save();
 
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTestBase.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTestBase.php
index 9fd5a34..3840c65 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTestBase.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TaxonomyTestBase.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\taxonomy\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -40,7 +40,7 @@ function createVocabulary() {
       'name' => $this->randomName(),
       'description' => $this->randomName(),
       'vid' => drupal_strtolower($this->randomName()),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'weight' => mt_rand(0, 10),
     ));
     $vocabulary->save();
@@ -61,7 +61,7 @@ function createTerm($vocabulary) {
         'format' => $format->format,
       ),
       'vid' => $vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term->save();
     return $term;
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermLanguageTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermLanguageTest.php
index 256a0a0..3da8b1b 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermLanguageTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermLanguageTest.php
@@ -63,7 +63,7 @@ function testTermLanguage() {
     $this->drupalPostForm(NULL, $edit, t('Save'));
     $terms = taxonomy_term_load_multiple_by_name($edit['name[0][value]']);
     $term = reset($terms);
-    $this->assertEqual($term->language()->id, $edit['langcode'], 'The term contains the correct langcode.');
+    $this->assertEqual($term->language()->getId(), $edit['langcode'], 'The term contains the correct langcode.');
 
     // Check if on the edit page the language is correct.
     $this->drupalGet('taxonomy/term/' . $term->id() . '/edit');
@@ -103,10 +103,10 @@ function testDefaultTermLanguage() {
     // Change the default language of the site and check if the default terms
     // language is still correctly selected.
     $old_default = \Drupal::languageManager()->getDefaultLanguage();
-    $old_default->default = FALSE;
+    $old_default->setDefault(FALSE);
     language_save($old_default);
     $new_default = \Drupal::languageManager()->getLanguage('cc');
-    $new_default->default = TRUE;
+    $new_default->setDefault(TRUE);
     language_save($new_default);
     $edit = array(
       'default_language[langcode]' => 'site_default',
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTranslationUITest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTranslationUITest.php
index a027ade..73033d5 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTranslationUITest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TermTranslationUITest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\taxonomy\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\content_translation\Tests\ContentTranslationUITest;
 
 /**
@@ -60,7 +60,7 @@ protected function setupBundle() {
       'name' => $this->bundle,
       'description' => $this->randomName(),
       'vid' => $this->bundle,
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'weight' => mt_rand(0, 10),
     ));
     $this->vocabulary->save();
@@ -128,7 +128,7 @@ function testTranslateLinkVocabularyAdminPage() {
       'name' => 'untranslatable_voc',
       'description' => $this->randomName(),
       'vid' => 'untranslatable_voc',
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'weight' => mt_rand(0, 10),
     ));
     $untranslatable_vocabulary->save();
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php
index a09cbc2..f2e72f41 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/TokenReplaceTest.php
@@ -9,7 +9,6 @@
 
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Component\Utility\String;
 
 /**
@@ -97,7 +96,7 @@ function testTaxonomyTokenReplacement() {
     $tests['[term:vocabulary:name]'] = String::checkPlain($this->vocabulary->name);
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('term' => $term1), array('langcode' => $language_interface->id));
+      $output = $token_service->replace($input, array('term' => $term1), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Sanitized taxonomy term token %token replaced.', array('%token' => $input)));
     }
 
@@ -117,7 +116,7 @@ function testTaxonomyTokenReplacement() {
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('term' => $term2), array('langcode' => $language_interface->id));
+      $output = $token_service->replace($input, array('term' => $term2), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Sanitized taxonomy term token %token replaced.', array('%token' => $input)));
     }
 
@@ -128,7 +127,7 @@ function testTaxonomyTokenReplacement() {
     $tests['[term:vocabulary:name]'] = $this->vocabulary->name;
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('term' => $term2), array('langcode' => $language_interface->id, 'sanitize' => FALSE));
+      $output = $token_service->replace($input, array('term' => $term2), array('langcode' => $language_interface->getId(), 'sanitize' => FALSE));
       $this->assertEqual($output, $expected, format_string('Unsanitized taxonomy term token %token replaced.', array('%token' => $input)));
     }
 
@@ -144,7 +143,7 @@ function testTaxonomyTokenReplacement() {
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('vocabulary' => $this->vocabulary), array('langcode' => $language_interface->id));
+      $output = $token_service->replace($input, array('vocabulary' => $this->vocabulary), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Sanitized taxonomy vocabulary token %token replaced.', array('%token' => $input)));
     }
 
@@ -153,7 +152,7 @@ function testTaxonomyTokenReplacement() {
     $tests['[vocabulary:description]'] = $this->vocabulary->description;
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('vocabulary' => $this->vocabulary), array('langcode' => $language_interface->id, 'sanitize' => FALSE));
+      $output = $token_service->replace($input, array('vocabulary' => $this->vocabulary), array('langcode' => $language_interface->getId(), 'sanitize' => FALSE));
       $this->assertEqual($output, $expected, format_string('Unsanitized taxonomy vocabulary token %token replaced.', array('%token' => $input)));
     }
   }
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php
index 2cc992e..587f4ce 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/Views/TaxonomyTestBase.php
@@ -8,7 +8,7 @@
 namespace Drupal\taxonomy\Tests\Views;
 
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\views\Tests\ViewTestBase;
 use Drupal\views\Tests\ViewTestData;
 
@@ -136,7 +136,7 @@ protected function createTerm() {
       // Use the first available text format.
       'format' => $format->format,
       'vid' => $this->vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term->save();
     return $term;
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/VocabularyForm.php b/core/modules/taxonomy/lib/Drupal/taxonomy/VocabularyForm.php
index 341bcbe..7287055 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/VocabularyForm.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/VocabularyForm.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Base form for vocabulary edit forms.
@@ -57,7 +57,7 @@ public function form(array $form, array &$form_state) {
     $form['langcode'] = array(
       '#type' => 'language_select',
       '#title' => $this->t('Vocabulary language'),
-      '#languages' => Language::STATE_ALL,
+      '#languages' => LanguageInterface::STATE_ALL,
       '#default_value' => $vocabulary->langcode,
     );
     if ($this->moduleHandler->moduleExists('language')) {
diff --git a/core/modules/taxonomy/taxonomy.module b/core/modules/taxonomy/taxonomy.module
index 4577e7e..b365c52 100644
--- a/core/modules/taxonomy/taxonomy.module
+++ b/core/modules/taxonomy/taxonomy.module
@@ -781,7 +781,7 @@ function taxonomy_build_node_index($node) {
       $field_name = $field->getName();
       if ($field->getType() == 'taxonomy_term_reference') {
         foreach ($node->getTranslationLanguages() as $language) {
-          foreach ($node->getTranslation($language->id)->$field_name as $item) {
+          foreach ($node->getTranslation($language->getId())->$field_name as $item) {
             if (!$item->isEmpty()) {
               $tid_all[$item->target_id] = $item->target_id;
             }
diff --git a/core/modules/text/lib/Drupal/text/Tests/Formatter/TextPlainUnitTest.php b/core/modules/text/lib/Drupal/text/Tests/Formatter/TextPlainUnitTest.php
index 8e37920..507874c 100644
--- a/core/modules/text/lib/Drupal/text/Tests/Formatter/TextPlainUnitTest.php
+++ b/core/modules/text/lib/Drupal/text/Tests/Formatter/TextPlainUnitTest.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\DrupalUnitTestBase;
 
 /**
@@ -92,7 +92,7 @@ function setUp() {
       ));
     $this->display->save();
 
-    $this->langcode = Language::LANGCODE_NOT_SPECIFIED;
+    $this->langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED;
   }
 
   /**
diff --git a/core/modules/text/lib/Drupal/text/Tests/TextWithSummaryItemTest.php b/core/modules/text/lib/Drupal/text/Tests/TextWithSummaryItemTest.php
index 9b93095..36008fc 100644
--- a/core/modules/text/lib/Drupal/text/Tests/TextWithSummaryItemTest.php
+++ b/core/modules/text/lib/Drupal/text/Tests/TextWithSummaryItemTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\text\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FieldItemInterface;
 use Drupal\field\Tests\FieldUnitTestBase;
@@ -128,7 +128,7 @@ function testProcessedCache() {
     $entity = entity_load($entity_type, $entity->id());
     $cache = \Drupal::cache('entity')->get("field:$entity_type:" . $entity->id());
     $this->assertEqual($cache->data, array(
-      Language::LANGCODE_NOT_SPECIFIED => array(
+      LanguageInterface::LANGCODE_NOT_SPECIFIED => array(
         'summary_field' => array(
           0 => array(
             'value' => $value,
@@ -144,7 +144,7 @@ function testProcessedCache() {
     // Inject fake processed values into the cache to make sure that these are
     // used as-is and not re-calculated when the entity is loaded.
     $data = array(
-      Language::LANGCODE_NOT_SPECIFIED => array(
+      LanguageInterface::LANGCODE_NOT_SPECIFIED => array(
         'summary_field' => array(
           0 => array(
             'value' => $value,
diff --git a/core/modules/toolbar/toolbar.module b/core/modules/toolbar/toolbar.module
index 3599c59..d09660e 100644
--- a/core/modules/toolbar/toolbar.module
+++ b/core/modules/toolbar/toolbar.module
@@ -6,7 +6,6 @@
  */
 
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Template\Attribute;
 use Drupal\Component\Utility\Crypt;
@@ -374,7 +373,7 @@ function toolbar_toolbar() {
   // toolbar_subtrees route. We provide the JavaScript requesting that JSONP
   // script here with the hash parameter that is needed for that route.
   // @see toolbar_subtrees_jsonp()
-  $langcode = \Drupal::languageManager()->getCurrentLanguage()->id;
+  $langcode = \Drupal::languageManager()->getCurrentLanguage()->getId();
   $menu['toolbar_administration']['#attached']['js'][] = array(
     'type' => 'setting',
     'data' => array('toolbar' => array(
diff --git a/core/modules/tracker/lib/Drupal/tracker/Tests/Views/TrackerTestBase.php b/core/modules/tracker/lib/Drupal/tracker/Tests/Views/TrackerTestBase.php
index a727ad5..7f20868 100644
--- a/core/modules/tracker/lib/Drupal/tracker/Tests/Views/TrackerTestBase.php
+++ b/core/modules/tracker/lib/Drupal/tracker/Tests/Views/TrackerTestBase.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\tracker\Tests\Views;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\views\Tests\ViewTestBase;
 use Drupal\views\Tests\ViewTestData;
 
@@ -55,7 +55,7 @@ protected function setUp() {
       'entity_type' => 'node',
       'field_name' => 'comment',
       'subject' => $this->randomName(),
-      'comment_body[' . Language::LANGCODE_NOT_SPECIFIED . '][0][value]' => $this->randomName(20),
+      'comment_body[' . LanguageInterface::LANGCODE_NOT_SPECIFIED . '][0][value]' => $this->randomName(20),
     ));
 
   }
diff --git a/core/modules/update/update.fetch.inc b/core/modules/update/update.fetch.inc
index d456801..1d3340c 100644
--- a/core/modules/update/update.fetch.inc
+++ b/core/modules/update/update.fetch.inc
@@ -110,7 +110,7 @@ function _update_cron_notify() {
   if (!empty($params)) {
     $notify_list = $update_config->get('notification.emails');
     if (!empty($notify_list)) {
-      $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
+      $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
       foreach ($notify_list as $target) {
         if ($target_user = user_load_by_mail($target)) {
           $target_langcode = $target_user->getPreferredLangcode();
diff --git a/core/modules/user/lib/Drupal/user/AccountForm.php b/core/modules/user/lib/Drupal/user/AccountForm.php
index 42a2292..646cd86 100644
--- a/core/modules/user/lib/Drupal/user/AccountForm.php
+++ b/core/modules/user/lib/Drupal/user/AccountForm.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Entity\ContentEntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Entity\Query\QueryFactory;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 use Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin;
@@ -245,15 +245,15 @@ public function form(array $form, array &$form_state) {
       );
     }
 
-    $user_preferred_langcode = $register ? $language_interface->id : $account->getPreferredLangcode();
+    $user_preferred_langcode = $register ? $language_interface->getId() : $account->getPreferredLangcode();
 
-    $user_preferred_admin_langcode = $register ? $language_interface->id : $account->getPreferredAdminLangcode();
+    $user_preferred_admin_langcode = $register ? $language_interface->getId() : $account->getPreferredAdminLangcode();
 
     // Is the user preferred language added?
     $user_language_added = FALSE;
     if ($this->languageManager instanceof ConfigurableLanguageManagerInterface) {
       $negotiator = $this->languageManager->getNegotiator();
-      $user_language_added = $negotiator && $negotiator->isNegotiationMethodEnabled(LanguageNegotiationUser::METHOD_ID, Language::TYPE_INTERFACE);
+      $user_language_added = $negotiator && $negotiator->isNegotiationMethodEnabled(LanguageNegotiationUser::METHOD_ID, LanguageInterface::TYPE_INTERFACE);
     }
     $form['language'] = array(
       '#type' => $this->languageManager->isMultilingual() ? 'details' : 'container',
@@ -267,7 +267,7 @@ public function form(array $form, array &$form_state) {
     $form['language']['preferred_langcode'] = array(
       '#type' => 'language_select',
       '#title' => $this->t('Site language'),
-      '#languages' => Language::STATE_CONFIGURABLE,
+      '#languages' => LanguageInterface::STATE_CONFIGURABLE,
       '#default_value' => $user_preferred_langcode,
       '#description' => $user_language_added ? $this->t("This account's preferred language for e-mails and site presentation.") : $this->t("This account's preferred language for e-mails."),
     );
@@ -282,7 +282,7 @@ public function form(array $form, array &$form_state) {
     $form['language']['preferred_admin_langcode'] = array(
       '#type' => 'language_select',
       '#title' => $this->t('Administration pages language'),
-      '#languages' => Language::STATE_CONFIGURABLE,
+      '#languages' => LanguageInterface::STATE_CONFIGURABLE,
       '#default_value' => $user_preferred_admin_langcode,
       '#access' => $show_admin_language,
     );
diff --git a/core/modules/user/lib/Drupal/user/Entity/User.php b/core/modules/user/lib/Drupal/user/Entity/User.php
index 25eb641..ecb45f7 100644
--- a/core/modules/user/lib/Drupal/user/Entity/User.php
+++ b/core/modules/user/lib/Drupal/user/Entity/User.php
@@ -377,10 +377,10 @@ function getPreferredLangcode($default = NULL) {
     $language_list = language_list();
     $preferred_langcode = $this->get('preferred_langcode')->value;
     if (!empty($preferred_langcode) && isset($language_list[$preferred_langcode])) {
-      return $language_list[$preferred_langcode]->id;
+      return $language_list[$preferred_langcode]->getId();
     }
     else {
-      return $default ? $default : language_default()->id;
+      return $default ? $default : language_default()->getId();
     }
   }
 
@@ -391,10 +391,10 @@ function getPreferredAdminLangcode($default = NULL) {
     $language_list = language_list();
     $preferred_langcode = $this->get('preferred_admin_langcode')->value;
     if (!empty($preferred_langcode) && isset($language_list[$preferred_langcode])) {
-      return $language_list[$preferred_langcode]->id;
+      return $language_list[$preferred_langcode]->getId();
     }
     else {
-      return $default ? $default : language_default()->id;
+      return $default ? $default : language_default()->getId();
     }
   }
 
diff --git a/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php b/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php
index 15d48c8..57b7764 100644
--- a/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php
+++ b/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php
@@ -9,7 +9,6 @@
 
 use Drupal\Core\Field\Plugin\Field\FieldType\EmailItem;
 use Drupal\Core\Form\FormBase;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\user\UserStorageInterface;
 use Symfony\Component\HttpFoundation\Request;
@@ -128,7 +127,7 @@ public function validateForm(array &$form, array &$form_state) {
    * {@inheritdoc}
    */
   public function submitForm(array &$form, array &$form_state) {
-    $langcode = $this->languageManager->getCurrentLanguage()->id;
+    $langcode = $this->languageManager->getCurrentLanguage()->getId();
 
     $account = $form_state['values']['account'];
     // Mail one time login URL and instructions using current language.
diff --git a/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUser.php b/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUser.php
index f2c99fe..623dac6 100644
--- a/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUser.php
+++ b/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUser.php
@@ -36,7 +36,7 @@ public function getLangcode(Request $request = NULL) {
     // User preference (only for authenticated users).
     if ($this->languageManager && $this->currentUser->isAuthenticated()) {
       $preferred_langcode = $this->currentUser->getPreferredLangcode();
-      $default_langcode = $this->languageManager->getDefaultLanguage()->id;
+      $default_langcode = $this->languageManager->getDefaultLanguage()->getId();
       $languages = $this->languageManager->getLanguages();
       if (!empty($preferred_langcode) && $preferred_langcode != $default_langcode && isset($languages[$preferred_langcode])) {
         $langcode = $preferred_langcode;
diff --git a/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php b/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php
index 50ed5a9..89fede5 100644
--- a/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php
+++ b/core/modules/user/lib/Drupal/user/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php
@@ -20,7 +20,7 @@
  *
  * @Plugin(
  *   id = Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin::METHOD_ID,
- *   types = {Drupal\Core\Language\Language::TYPE_INTERFACE},
+ *   types = {Drupal\Core\Language\LanguageInterface::TYPE_INTERFACE},
  *   weight = 10,
  *   name = @Translation("Account administration pages"),
  *   description = @Translation("Account administration pages language setting.")
@@ -82,7 +82,7 @@ public function getLangcode(Request $request = NULL) {
     // User preference (only for authenticated users).
     if ($this->languageManager && $this->currentUser->isAuthenticated() && $this->isAdminPath($request)) {
       $preferred_admin_langcode = $this->currentUser->getPreferredAdminLangcode();
-      $default_langcode = $this->languageManager->getDefaultLanguage()->id;
+      $default_langcode = $this->languageManager->getDefaultLanguage()->getId();
       $languages = $this->languageManager->getLanguages();
       if (!empty($preferred_admin_langcode) && $preferred_admin_langcode != $default_langcode && isset($languages[$preferred_admin_langcode])) {
         $langcode = $preferred_admin_langcode;
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserEntityTest.php b/core/modules/user/lib/Drupal/user/Tests/UserEntityTest.php
index 43bee29..9621d33 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserEntityTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserEntityTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\user\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\DrupalUnitTestBase;
 use Drupal\user\Entity\User;
 
@@ -46,7 +46,7 @@ public function testUserMethods() {
     $role_storage->create(array('id' => 'test_role_two'))->save();
     $role_storage->create(array('id' => 'test_role_three'))->save();
 
-    $values = array('roles' => array(Language::LANGCODE_DEFAULT => array('test_role_one')));
+    $values = array('roles' => array(LanguageInterface::LANGCODE_DEFAULT => array('test_role_one')));
     $user = new User($values, 'user');
 
     $this->assertTrue($user->hasRole('test_role_one'));
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserInstallTest.php b/core/modules/user/lib/Drupal/user/Tests/UserInstallTest.php
index 7014a03..3fb16fd 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserInstallTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserInstallTest.php
@@ -53,8 +53,8 @@ public function testUserInstall() {
 
     // Test that the anonymous and administrators languages are equal to the
     // site's default language.
-    $this->assertEqual($anon->langcode, \Drupal::languageManager()->getDefaultLanguage()->id);
-    $this->assertEqual($admin->langcode, \Drupal::languageManager()->getDefaultLanguage()->id);
+    $this->assertEqual($anon->langcode, \Drupal::languageManager()->getDefaultLanguage()->getId(), 'Anon user language is the default.');
+    $this->assertEqual($admin->langcode, \Drupal::languageManager()->getDefaultLanguage()->getId(), 'Admin user language is the default.');
 
     // Test that the administrator is active.
     $this->assertEqual($admin->status, 1);
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserLanguageCreationTest.php b/core/modules/user/lib/Drupal/user/Tests/UserLanguageCreationTest.php
index dbf80e4..2360b7b 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserLanguageCreationTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserLanguageCreationTest.php
@@ -69,7 +69,7 @@ function testLocalUserCreation() {
 
     $user = user_load_by_name($username);
     $this->assertEqual($user->getPreferredLangcode(), $langcode, 'New user has correct preferred language set.');
-    $this->assertEqual($user->language()->id, $langcode, 'New user has correct profile language set.');
+    $this->assertEqual($user->language()->getId(), $langcode, 'New user has correct profile language set.');
 
     // Register a new user and check if the language selector is hidden.
     $this->drupalLogout();
@@ -87,7 +87,7 @@ function testLocalUserCreation() {
 
     $user = user_load_by_name($username);
     $this->assertEqual($user->getPreferredLangcode(), $langcode, 'New user has correct preferred language set.');
-    $this->assertEqual($user->language()->id, $langcode, 'New user has correct profile language set.');
+    $this->assertEqual($user->language()->getId(), $langcode, 'New user has correct profile language set.');
 
     // Test if the admin can use the language selector and if the
     // correct language is was saved.
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
index a0b205c..6c07b09 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\user\Tests;
 
 use Drupal\Core\Field\FieldDefinitionInterface;
-use Drupal\Core\Language\Language;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -189,8 +188,8 @@ function testRegistrationDefaultValues() {
     $this->assertTrue(($new_user->getCreatedTime() > REQUEST_TIME - 20 ), 'Correct creation time.');
     $this->assertEqual($new_user->isActive(), $config_user_settings->get('register') == USER_REGISTER_VISITORS ? 1 : 0, 'Correct status field.');
     $this->assertEqual($new_user->getTimezone(), $config_system_date->get('timezone.default'), 'Correct time zone field.');
-    $this->assertEqual($new_user->langcode->value, \Drupal::languageManager()->getDefaultLanguage()->id, 'Correct language field.');
-    $this->assertEqual($new_user->preferred_langcode->value, \Drupal::languageManager()->getDefaultLanguage()->id, 'Correct preferred language field.');
+    $this->assertEqual($new_user->langcode->value, \Drupal::languageManager()->getDefaultLanguage()->getId(), 'Correct language field.');
+    $this->assertEqual($new_user->preferred_langcode->value, \Drupal::languageManager()->getDefaultLanguage()->getId(), 'Correct preferred language field.');
     $this->assertEqual($new_user->init->value, $mail, 'Correct init field.');
   }
 
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserRoleAdminTest.php b/core/modules/user/lib/Drupal/user/Tests/UserRoleAdminTest.php
index 0ddfa73..04361b2 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserRoleAdminTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserRoleAdminTest.php
@@ -32,7 +32,7 @@ function setUp() {
    */
   function testRoleAdministration() {
     $this->drupalLogin($this->admin_user);
-    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
+    $default_langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
     // Test presence of tab.
     $this->drupalGet('admin/people/permissions');
     $tabs = $this->xpath('//ul[@class=:classes and //a[contains(., :text)]]', array(
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserTokenReplaceTest.php b/core/modules/user/lib/Drupal/user/Tests/UserTokenReplaceTest.php
index c9be29c..e87fbe1 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserTokenReplaceTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserTokenReplaceTest.php
@@ -66,17 +66,17 @@ function testUserTokenReplacement() {
     $tests['[user:mail]'] = check_plain($account->getEmail());
     $tests['[user:url]'] = url("user/" . $account->id(), $url_options);
     $tests['[user:edit-url]'] = url("user/" . $account->id() . "/edit", $url_options);
-    $tests['[user:last-login]'] = format_date($account->getLastLoginTime(), 'medium', '', NULL, $language_interface->id);
-    $tests['[user:last-login:short]'] = format_date($account->getLastLoginTime(), 'short', '', NULL, $language_interface->id);
-    $tests['[user:created]'] = format_date($account->getCreatedTime(), 'medium', '', NULL, $language_interface->id);
-    $tests['[user:created:short]'] = format_date($account->getCreatedTime(), 'short', '', NULL, $language_interface->id);
+    $tests['[user:last-login]'] = format_date($account->getLastLoginTime(), 'medium', '', NULL, $language_interface->getId());
+    $tests['[user:last-login:short]'] = format_date($account->getLastLoginTime(), 'short', '', NULL, $language_interface->getId());
+    $tests['[user:created]'] = format_date($account->getCreatedTime(), 'medium', '', NULL, $language_interface->getId());
+    $tests['[user:created:short]'] = format_date($account->getCreatedTime(), 'short', '', NULL, $language_interface->getId());
     $tests['[current-user:name]'] = check_plain(user_format_name($global_account));
 
     // Test to make sure that we generated something for each token.
     $this->assertFalse(in_array(0, array_map('strlen', $tests)), 'No empty tokens generated.');
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('user' => $account), array('langcode' => $language_interface->id));
+      $output = $token_service->replace($input, array('user' => $account), array('langcode' => $language_interface->getId()));
       $this->assertEqual($output, $expected, format_string('Sanitized user token %token replaced.', array('%token' => $input)));
     }
 
@@ -86,7 +86,7 @@ function testUserTokenReplacement() {
     $tests['[current-user:name]'] = user_format_name($global_account);
 
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('user' => $account), array('langcode' => $language_interface->id, 'sanitize' => FALSE));
+      $output = $token_service->replace($input, array('user' => $account), array('langcode' => $language_interface->getId(), 'sanitize' => FALSE));
       $this->assertEqual($output, $expected, format_string('Unsanitized user token %token replaced.', array('%token' => $input)));
     }
 
@@ -98,7 +98,7 @@ function testUserTokenReplacement() {
     // Generate tokens with interface language.
     $link = url('user', array('absolute' => TRUE));
     foreach ($tests as $input => $expected) {
-      $output = $token_service->replace($input, array('user' => $account), array('langcode' => $language_interface->id, 'callback' => 'user_mail_tokens', 'sanitize' => FALSE, 'clear' => TRUE));
+      $output = $token_service->replace($input, array('user' => $account), array('langcode' => $language_interface->getId(), 'callback' => 'user_mail_tokens', 'sanitize' => FALSE, 'clear' => TRUE));
       $this->assertTrue(strpos($output, $link) === 0, 'Generated URL is in interface language.');
     }
 
diff --git a/core/modules/user/user.install b/core/modules/user/user.install
index 086a5a0..db8dcde 100644
--- a/core/modules/user/user.install
+++ b/core/modules/user/user.install
@@ -220,7 +220,7 @@ function user_install() {
   $storage = \Drupal::entityManager()->getStorage('user');
   // @todo Rely on the default value for langcode in
   //   https://drupal.org/node/1966436
-  $langcode = \Drupal::languageManager()->getDefaultLanguage()->id;
+  $langcode = \Drupal::languageManager()->getDefaultLanguage()->getId();
   // Insert a row for the anonymous user.
   $storage
     ->create(array(
diff --git a/core/modules/user/user.module b/core/modules/user/user.module
index 3fe1f1c..db87621 100644
--- a/core/modules/user/user.module
+++ b/core/modules/user/user.module
@@ -1472,7 +1472,7 @@ function _user_mail_notify($op, $account, $langcode = NULL) {
     if ($op == 'register_pending_approval') {
       // If a user registered requiring admin approval, notify the admin, too.
       // We use the site default language for this.
-      drupal_mail('user', 'register_pending_approval_admin', $site_mail, \Drupal::languageManager()->getDefaultLanguage()->id, $params);
+      drupal_mail('user', 'register_pending_approval_admin', $site_mail, \Drupal::languageManager()->getDefaultLanguage()->getId(), $params);
     }
   }
   return empty($mail) ? NULL : $mail['result'];
diff --git a/core/modules/views/lib/Drupal/views/Entity/Render/DefaultLanguageRenderer.php b/core/modules/views/lib/Drupal/views/Entity/Render/DefaultLanguageRenderer.php
index 18875f5..2e99c12 100644
--- a/core/modules/views/lib/Drupal/views/Entity/Render/DefaultLanguageRenderer.php
+++ b/core/modules/views/lib/Drupal/views/Entity/Render/DefaultLanguageRenderer.php
@@ -24,7 +24,7 @@ class DefaultLanguageRenderer extends RendererBase {
    *   A language code.
    */
   protected function getLangcode(ResultRow $row) {
-    return $row->_entity->getUntranslated()->language()->id;
+    return $row->_entity->getUntranslated()->language()->getId();
   }
 
 }
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/cache/CachePluginBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/cache/CachePluginBase.php
index 4f2503c..38ff388 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/cache/CachePluginBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/cache/CachePluginBase.php
@@ -8,7 +8,6 @@
 namespace Drupal\views\Plugin\views\cache;
 
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
 use Drupal\views\Plugin\views\PluginBase;
 use Drupal\Core\Database\Query\Select;
 
@@ -294,7 +293,7 @@ public function generateResultsKey() {
         'build_info' => $build_info,
         'roles' => $user->getRoles(),
         'super-user' => $user->id() == 1, // special caching for super user.
-        'langcode' => \Drupal::languageManager()->getCurrentLanguage()->id,
+        'langcode' => \Drupal::languageManager()->getCurrentLanguage()->getId(),
         'base_url' => $GLOBALS['base_url'],
       );
       $request = \Drupal::request();
@@ -324,7 +323,7 @@ public function generateOutputKey() {
         'roles' => $user->getRoles(),
         'super-user' => $user->id() == 1, // special caching for super user.
         'theme' => $GLOBALS['theme'],
-        'langcode' => \Drupal::languageManager()->getCurrentLanguage()->id,
+        'langcode' => \Drupal::languageManager()->getCurrentLanguage()->getId(),
         'base_url' => $GLOBALS['base_url'],
       );
 
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/display/DisplayPluginBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/display/DisplayPluginBase.php
index 750546f..a8c650a 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/display/DisplayPluginBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/display/DisplayPluginBase.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Core\Cache\Cache;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Theme\Registry;
 use Drupal\views\Plugin\views\area\AreaPluginBase;
@@ -158,7 +158,7 @@ public function initDisplay(ViewExecutable $view, array &$display, array &$optio
     $skip_cache = \Drupal::config('views.settings')->get('skip_cache');
 
     if (empty($view->editing) || !$skip_cache) {
-      $cid = 'views:unpack_options:' . hash('sha256', serialize(array($this->options, $options))) . ':' . \Drupal::languageManager()->getCurrentLanguage()->id;
+      $cid = 'views:unpack_options:' . hash('sha256', serialize(array($this->options, $options))) . ':' . \Drupal::languageManager()->getCurrentLanguage()->getId();
       if (empty(static::$unpackOptions[$cid])) {
         $cache = \Drupal::cache('data')->get($cid);
         if (!empty($cache->data)) {
@@ -1243,7 +1243,7 @@ public function optionsSummary(&$categories, &$options) {
     $languages = array(
         '***CURRENT_LANGUAGE***' => t("Current user's language"),
         '***DEFAULT_LANGUAGE***' => t("Default site language"),
-        Language::LANGCODE_NOT_SPECIFIED => t('Language neutral'),
+        LanguageInterface::LANGCODE_NOT_SPECIFIED => t('Language neutral'),
     );
     if (\Drupal::moduleHandler()->moduleExists('language')) {
       $languages = array_merge($languages, language_list());
@@ -1617,7 +1617,7 @@ public function buildOptionsForm(&$form, &$form_state) {
           $languages = array(
             '***CURRENT_LANGUAGE***' => t("Current user's language"),
             '***DEFAULT_LANGUAGE***' => t("Default site language"),
-            Language::LANGCODE_NOT_SPECIFIED => t('Language neutral'),
+            LanguageInterface::LANGCODE_NOT_SPECIFIED => t('Language neutral'),
           );
           $languages = array_merge($languages, views_language_list());
 
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/wizard/WizardPluginBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/wizard/WizardPluginBase.php
index 4ed08e4..c31217f 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/wizard/WizardPluginBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/wizard/WizardPluginBase.php
@@ -634,7 +634,7 @@ protected function instantiateView($form, &$form_state) {
       'label' => $form_state['values']['label'],
       'description' => $form_state['values']['description'],
       'base_table' => $this->base_table,
-      'langcode' => language_default()->id,
+      'langcode' => language_default()->getId(),
     );
 
     $view = entity_create('view', $values);
diff --git a/core/modules/views/lib/Drupal/views/Tests/DefaultViewsTest.php b/core/modules/views/lib/Drupal/views/Tests/DefaultViewsTest.php
index 6e74149..513c3b2 100644
--- a/core/modules/views/lib/Drupal/views/Tests/DefaultViewsTest.php
+++ b/core/modules/views/lib/Drupal/views/Tests/DefaultViewsTest.php
@@ -8,7 +8,7 @@
 namespace Drupal\views\Tests;
 
 use Drupal\comment\CommentInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 use Drupal\views\ViewExecutable;
 use Drupal\views\Views;
@@ -54,7 +54,7 @@ protected function setUp() {
       'name' => $this->randomName(),
       'description' => $this->randomName(),
       'vid' => drupal_strtolower($this->randomName()),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
       'help' => '',
       'nodes' => array('page' => 'page'),
       'weight' => mt_rand(0, 10),
@@ -164,7 +164,7 @@ function createTerm($vocabulary) {
       // Use the first available text format.
       'format' => $format->format,
       'vid' => $vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term->save();
     return $term;
diff --git a/core/modules/views/lib/Drupal/views/Tests/Entity/RowEntityRenderersTest.php b/core/modules/views/lib/Drupal/views/Tests/Entity/RowEntityRenderersTest.php
index 869ad88..3147d5f 100644
--- a/core/modules/views/lib/Drupal/views/Tests/Entity/RowEntityRenderersTest.php
+++ b/core/modules/views/lib/Drupal/views/Tests/Entity/RowEntityRenderersTest.php
@@ -63,7 +63,7 @@ protected function setUp() {
     // The node.view route must exist when nodes are rendered.
     $this->container->get('router.builder')->rebuild();
 
-    $this->langcodes = array(\Drupal::languageManager()->getDefaultLanguage()->id);
+    $this->langcodes = array(\Drupal::languageManager()->getDefaultLanguage()->getId());
     for ($i = 0; $i < 2; $i++) {
       $langcode = 'l' . $i;
       $this->langcodes[] = $langcode;
diff --git a/core/modules/views/lib/Drupal/views/Tests/Handler/AreaEntityTest.php b/core/modules/views/lib/Drupal/views/Tests/Handler/AreaEntityTest.php
index 5751042..f2a42fc 100644
--- a/core/modules/views/lib/Drupal/views/Tests/Handler/AreaEntityTest.php
+++ b/core/modules/views/lib/Drupal/views/Tests/Handler/AreaEntityTest.php
@@ -8,7 +8,6 @@
 namespace Drupal\views\Tests\Handler;
 
 use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Language\Language;
 use Drupal\views\Tests\ViewTestBase;
 use Drupal\views\Views;
 
diff --git a/core/modules/views/lib/Drupal/views/Tests/ViewsTaxonomyAutocompleteTest.php b/core/modules/views/lib/Drupal/views/Tests/ViewsTaxonomyAutocompleteTest.php
index 766ae49..98611a7 100644
--- a/core/modules/views/lib/Drupal/views/Tests/ViewsTaxonomyAutocompleteTest.php
+++ b/core/modules/views/lib/Drupal/views/Tests/ViewsTaxonomyAutocompleteTest.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\views\Tests\ViewTestBase;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Tests the views taxonomy complete menu callback.
@@ -105,7 +105,7 @@ protected function createTerm($name = NULL) {
       'name' => $name ?: $this->randomName(),
       'description' => $this->randomName(),
       'vid' => $this->vocabulary->id(),
-      'langcode' => Language::LANGCODE_NOT_SPECIFIED,
+      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ));
     $term->save();
     return $term;
diff --git a/core/modules/views/lib/Drupal/views/ViewAccessController.php b/core/modules/views/lib/Drupal/views/ViewAccessController.php
index e761af2..3b22203 100644
--- a/core/modules/views/lib/Drupal/views/ViewAccessController.php
+++ b/core/modules/views/lib/Drupal/views/ViewAccessController.php
@@ -9,7 +9,6 @@
 
 use Drupal\Core\Entity\EntityAccessController;
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Session\AccountInterface;
 
 /**
diff --git a/core/modules/views/lib/Drupal/views/ViewsData.php b/core/modules/views/lib/Drupal/views/ViewsData.php
index 3fccb8f..f329c36 100644
--- a/core/modules/views/lib/Drupal/views/ViewsData.php
+++ b/core/modules/views/lib/Drupal/views/ViewsData.php
@@ -96,7 +96,7 @@ public function __construct(CacheBackendInterface $cache_backend, ConfigFactoryI
     $this->moduleHandler = $module_handler;
     $this->languageManager = $language_manager;
 
-    $this->langcode = $this->languageManager->getCurrentLanguage()->id;
+    $this->langcode = $this->languageManager->getCurrentLanguage()->getId();
     $this->skipCache = $config->get('views.settings')->get('skip_cache');
   }
 
diff --git a/core/modules/views/views.api.php b/core/modules/views/views.api.php
index f1551e2..1763c19 100644
--- a/core/modules/views/views.api.php
+++ b/core/modules/views/views.api.php
@@ -341,8 +341,8 @@ function hook_views_query_substitutions(ViewExecutable $view) {
   return array(
     '***CURRENT_VERSION***' => \Drupal::VERSION,
     '***CURRENT_TIME***' => REQUEST_TIME,
-    '***CURRENT_LANGUAGE***' => \Drupal::languageManager()->getCurrentLanguage(\Drupal\Core\Language\Language::TYPE_CONTENT)->id,
-    '***DEFAULT_LANGUAGE***' => \Drupal::languageManager()->getDefaultLanguage()->id,
+    '***CURRENT_LANGUAGE***' => \Drupal::languageManager()->getCurrentLanguage(\Drupal\Core\Language\LanguageInterface::TYPE_CONTENT)->getId(),
+    '***DEFAULT_LANGUAGE***' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
   );
 }
 
diff --git a/core/modules/views/views.module b/core/modules/views/views.module
index 216bc93..758efac 100644
--- a/core/modules/views/views.module
+++ b/core/modules/views/views.module
@@ -12,7 +12,7 @@
 use Drupal\Component\Utility\String;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Database\Query\AlterableInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Render\Element;
 use Drupal\views\Plugin\Derivative\ViewsLocalTask;
 use Drupal\Core\Template\AttributeArray;
@@ -507,19 +507,19 @@ function views_add_contextual_links(&$render_element, $location, ViewExecutable
  *   array.
  * @param int $flags
  *   (optional) Specifies the state of the languages that have to be returned.
- *   It can be: Language::STATE_CONFIGURABLE, Language::STATE_LOCKED,
- *   Language::STATE_ALL.
+ *   It can be: LanguageInterface::STATE_CONFIGURABLE, LanguageInterface::STATE_LOCKED,
+ *   LanguageInterface::STATE_ALL.
  *
  * @return array
  *   An array of language names (or $field) keyed by the langcode.
  *
  * @see locale_language_list()
  */
-function views_language_list($field = 'name', $flags = Language::STATE_ALL) {
+function views_language_list($field = 'name', $flags = LanguageInterface::STATE_ALL) {
   $languages = \Drupal::languageManager()->getLanguages($flags);
   $list = array();
   foreach ($languages as $language) {
-    $list[$language->id] = ($field == 'name') ? t($language->name) : $language->$field;
+    $list[$language->getId()] = ($field == 'name') ? t($language->getName()) : $language->$field;
   }
   return $list;
 }
diff --git a/core/modules/views/views.theme.inc b/core/modules/views/views.theme.inc
index ae967bd..52cf376 100644
--- a/core/modules/views/views.theme.inc
+++ b/core/modules/views/views.theme.inc
@@ -7,7 +7,6 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Xss;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Template\Attribute;
 use Drupal\views\Form\ViewsForm;
 use Drupal\views\ViewExecutable;
@@ -968,7 +967,7 @@ function template_preprocess_views_view_rss(&$variables) {
     $variables['link'] = check_url(url($path, $url_options));
   }
 
-  $variables['langcode'] = String::checkPlain(\Drupal::languageManager()->getCurrentLanguage()->id);
+  $variables['langcode'] = String::checkPlain(\Drupal::languageManager()->getCurrentLanguage()->getId());
   $variables['namespaces'] = new Attribute($style->namespaces);
   $variables['items'] = $items;
   $variables['channel_elements'] = format_xml_elements($style->channel_elements);
diff --git a/core/modules/views/views.views_execution.inc b/core/modules/views/views.views_execution.inc
index d1c040f..1c4f5bc 100644
--- a/core/modules/views/views.views_execution.inc
+++ b/core/modules/views/views.views_execution.inc
@@ -5,7 +5,7 @@
  * Provides views runtime hooks for views.module.
  */
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\views\ViewExecutable;
 
 /**
@@ -17,7 +17,7 @@ function views_views_query_substitutions(ViewExecutable $view) {
   return array(
     '***CURRENT_VERSION***' => \Drupal::VERSION,
     '***CURRENT_TIME***' => REQUEST_TIME,
-    '***CURRENT_LANGUAGE***' => \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT)->id,
-    '***DEFAULT_LANGUAGE***' => \Drupal::languageManager()->getDefaultLanguage()->id,
+    '***CURRENT_LANGUAGE***' => \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId(),
+    '***DEFAULT_LANGUAGE***' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
   );
 }
diff --git a/core/modules/views_ui/tests/Drupal/views_ui/Tests/ViewUIObjectTest.php b/core/modules/views_ui/tests/Drupal/views_ui/Tests/ViewUIObjectTest.php
index 7cbf7b9..f105b3a 100644
--- a/core/modules/views_ui/tests/Drupal/views_ui/Tests/ViewUIObjectTest.php
+++ b/core/modules/views_ui/tests/Drupal/views_ui/Tests/ViewUIObjectTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\views_ui\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Tests\UnitTestCase;
 use Drupal\views\ViewExecutable;
 use Drupal\views_ui\ViewUI;
@@ -37,7 +37,7 @@ public function testEntityDecoration() {
     $method_args['setOriginalId'] = array(12);
     $method_args['setStatus'] = array(TRUE);
     $method_args['enforceIsNew'] = array(FALSE);
-    $method_args['label'] = array(Language::LANGCODE_NOT_SPECIFIED);
+    $method_args['label'] = array(LanguageInterface::LANGCODE_NOT_SPECIFIED);
 
     $reflection = new \ReflectionClass('Drupal\Core\Config\Entity\ConfigEntityInterface');
     $interface_methods = array();
diff --git a/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
index 100ad29..fd82338 100644
--- a/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
@@ -17,6 +17,7 @@
 use Drupal\Core\Entity\EntityManager;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Tests\UnitTestCase;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -111,12 +112,16 @@ protected function setUp() {
 
     $this->cache = $this->getMock('Drupal\Core\Cache\CacheBackendInterface');
 
+    $language = $this->getMock('\Drupal\Core\Language\LanguageInterface');
+    $language->expects($this->any())
+      ->method('getId')
+      ->will($this->returnValue('en'));
     $this->languageManager = $this->getMockBuilder('Drupal\Core\Language\LanguageManager')
       ->disableOriginalConstructor()
       ->getMock();
     $this->languageManager->expects($this->any())
       ->method('getCurrentLanguage')
-      ->will($this->returnValue((object) array('id' => 'en')));
+      ->will($this->returnValue($language));
 
     $this->translationManager = $this->getStringTranslationStub();
 
@@ -890,13 +895,17 @@ public function testGetTranslationFromContext() {
     $entity->expects($this->exactly(2))
       ->method('getUntranslated')
       ->will($this->returnValue($entity));
+    $language = $this->getMock('\Drupal\Core\Language\LanguageInterface');
+    $language->expects($this->any())
+      ->method('getId')
+      ->will($this->returnValue('en'));
     $entity->expects($this->exactly(2))
       ->method('language')
-      ->will($this->returnValue((object) array('id' => 'en')));
+      ->will($this->returnValue($language));
     $entity->expects($this->exactly(2))
       ->method('hasTranslation')
       ->will($this->returnValueMap(array(
-        array(Language::LANGCODE_DEFAULT, FALSE),
+        array(LanguageInterface::LANGCODE_DEFAULT, FALSE),
         array('custom_langcode', TRUE),
       )));
 
@@ -937,7 +946,7 @@ function testgetExtraFields() {
     $cache_id = 'entity_bundle_extra_fields:' . $entity_type_id . ':' . $bundle . ':' . $language_code;
 
     $language = new Language();
-    $language->id = $language_code;
+    $language->setId($language_code);
 
     $this->languageManager->expects($this->once())
       ->method('getCurrentLanguage')
diff --git a/core/tests/Drupal/Tests/Core/Entity/EntityUnitTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityUnitTest.php
index 6ccad14..592b3cc 100644
--- a/core/tests/Drupal/Tests/Core/Entity/EntityUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/EntityUnitTest.php
@@ -236,7 +236,7 @@ public function testAccess() {
    * @covers ::language
    */
   public function testLanguage() {
-    $this->assertSame('en', $this->entity->language()->id);
+    $this->assertSame('en', $this->entity->language()->getId());
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Mail/MailManagerTest.php b/core/tests/Drupal/Tests/Core/Mail/MailManagerTest.php
index 9ef8d20..e5ba12a 100644
--- a/core/tests/Drupal/Tests/Core/Mail/MailManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Mail/MailManagerTest.php
@@ -91,9 +91,13 @@ protected function setUp() {
     $this->cache = $this->getMock('Drupal\Core\Cache\CacheBackendInterface');
 
     $this->languageManager = $this->getMock('Drupal\Core\Language\LanguageManagerInterface');
+    $language = $this->getMock('\Drupal\Core\Language\LanguageInterface');
+    $language->expects($this->any())
+      ->method('getId')
+      ->will($this->returnValue('en'));
     $this->languageManager->expects($this->any())
       ->method('getCurrentLanguage')
-      ->will($this->returnValue((object) array('id' => 'en')));
+      ->will($this->returnValue($language));
 
     $this->moduleHandler = $this->getMock('Drupal\Core\Extension\ModuleHandlerInterface');
 
diff --git a/core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php b/core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php
index f58edc5..de80260c0 100644
--- a/core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php
+++ b/core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\Tests\Core\PathProcessor;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\PathProcessor\PathProcessorAlias;
 use Drupal\Core\PathProcessor\PathProcessorDecode;
 use Drupal\Core\PathProcessor\PathProcessorFront;
@@ -26,6 +26,9 @@
  */
 class PathProcessorTest extends UnitTestCase {
 
+  /**
+   * @var \Drupal\Core\Language\LanguageInterface[]
+   */
   protected $languages;
   protected $languageManager;
 
@@ -42,9 +45,13 @@ public function setUp() {
     // Set up some languages to be used by the language-based path processor.
     $languages = array();
     foreach (array('en' => 'English', 'fr' => 'French') as $langcode => $language_name) {
-      $language = new \stdClass();
-      $language->id = $langcode;
-      $language->name = $language_name;
+      $language = $this->getMock('\Drupal\Core\Language\LanguageInterface');
+      $language->expects($this->any())
+        ->method('getId')
+        ->will($this->returnValue($langcode));
+      $language->expects($this->any())
+        ->method('getName')
+        ->will($this->returnValue($language_name));
       $languages[$langcode] = $language;
     }
     $this->languages = $languages;
@@ -78,7 +85,7 @@ public function setUp() {
       ->will($this->returnValue($this->languages));
     $language_manager->expects($this->any())
       ->method('getLanguageTypes')
-      ->will($this->returnValue(array(Language::TYPE_INTERFACE)));
+      ->will($this->returnValue(array(LanguageInterface::TYPE_INTERFACE)));
     $language_manager->expects($this->any())
       ->method('getNegotiationMethods')
       ->will($this->returnValue($method_definitions));
diff --git a/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php b/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
index 4862ac7..68c952c 100644
--- a/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\Tests\Core\Plugin;
 
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -143,7 +144,7 @@ public function testDefaultPluginManagerWithEmptyCache() {
     $language_manager = $this->getMock('Drupal\Core\Language\LanguageManagerInterface');
     $language_manager->expects($this->once())
       ->method('getCurrentLanguage')
-      ->with(Language::TYPE_INTERFACE)
+      ->with(LanguageInterface::TYPE_INTERFACE)
       ->will($this->returnValue($language));
 
     $plugin_manager = new TestPluginManager($this->namespaces, $this->expectedDefinitions);
@@ -174,7 +175,7 @@ public function testDefaultPluginManagerWithFilledCache() {
     $language_manager = $this->getMock('Drupal\Core\Language\LanguageManagerInterface');
     $language_manager->expects($this->once())
       ->method('getCurrentLanguage')
-      ->with(Language::TYPE_INTERFACE)
+      ->with(LanguageInterface::TYPE_INTERFACE)
       ->will($this->returnValue($language));
 
     $plugin_manager = new TestPluginManager($this->namespaces, $this->expectedDefinitions);
@@ -205,7 +206,7 @@ public function testCacheClearWithTags() {
     $language_manager = $this->getMock('Drupal\Core\Language\LanguageManagerInterface');
     $language_manager->expects($this->once())
       ->method('getCurrentLanguage')
-      ->with(Language::TYPE_INTERFACE)
+      ->with(LanguageInterface::TYPE_INTERFACE)
       ->will($this->returnValue($language));
 
     $plugin_manager = new TestPluginManager($this->namespaces, $this->expectedDefinitions);
diff --git a/core/tests/Drupal/Tests/Core/Utility/TokenTest.php b/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
index f92502e..980ca93 100644
--- a/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
+++ b/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\Tests\Core\Utility;
 
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Utility\Token;
 use Drupal\Tests\UnitTestCase;
 
@@ -83,7 +84,7 @@ public function testGetInfo() {
     );
 
     $language = $this->getMock('\Drupal\Core\Language\Language');
-    $language->id = $this->randomName();
+    $language->setId($this->randomName());
 
     $this->languageManager->expects($this->once())
       ->method('getCurrentLanguage')
@@ -96,7 +97,7 @@ public function testGetInfo() {
       ->method('get');
     $this->cache->expects($this->once())
       ->method('set')
-      ->with('token_info:' . $language->id, $token_info);
+      ->with('token_info:' . $language->getId(), $token_info);
 
     $this->moduleHandler->expects($this->once())
       ->method('invokeAll')