diff -u b/core/lib/Drupal/Core/Language/LanguageManager.php b/core/lib/Drupal/Core/Language/LanguageManager.php
--- b/core/lib/Drupal/Core/Language/LanguageManager.php
+++ b/core/lib/Drupal/Core/Language/LanguageManager.php
@@ -40,7 +40,7 @@
   /**
    * 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) {
diff -u b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php
--- b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php
@@ -15,7 +15,7 @@
 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;
@@ -351,7 +351,7 @@
   /**
    * 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.
@@ -375,7 +375,7 @@
    * @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.
diff -u b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/DateFormat.php b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/DateFormat.php
--- b/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;
 
 /**
  * Defines the date format element for the configuration translation interface.
@@ -20,7 +20,7 @@
   /**
    * {@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'));
     }
diff -u b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textarea.php b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textarea.php
--- b/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;
 
 /**
  * Defines the textarea element for the configuration translation interface.
@@ -17,7 +17,7 @@
   /**
    * {@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;
diff -u b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textfield.php b/core/modules/config_translation/lib/Drupal/config_translation/FormElement/Textfield.php
--- b/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;
 
 /**
  * Defines the textfield element for the configuration translation interface.
@@ -17,7 +17,7 @@
   /**
    * {@inheritdoc}
    */
-  public function getFormElement(array $definition, Language $language, $value) {
+  public function getFormElement(array $definition, LanguageInterface $language, $value) {
     return array(
       '#type' => 'textfield',
       '#default_value' => $value,
diff -u b/core/modules/content_translation/content_translation.pages.inc b/core/modules/content_translation/content_translation.pages.inc
--- b/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;
 
@@ -154,12 +154,13 @@
  *   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;
 }
@@ -169,10 +170,10 @@
  *
  * @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.
  *
@@ -182,9 +183,9 @@
  * @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->getId();
@@ -199,7 +200,7 @@
  *
  * @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.
  *
@@ -209,8 +210,8 @@
  * @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);
+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);
@@ -221,12 +222,12 @@
  *
  * @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->getId());
     $entity->addTranslation($target->getId(), $source_translation->toArray());
diff -u b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
--- b/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;
 
@@ -152,7 +152,7 @@
   /**
    * {@inheritdoc}
    */
-  public function setLanguage(Language $language = NULL) {
+  public function setLanguage(LanguageInterface $language = NULL) {
     $this->language = $language;
     return $this;
   }
diff -u b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodBase.php b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodBase.php
--- b/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;
 use Drupal\Core\Session\AccountInterface;
 
 /**
@@ -61,7 +61,7 @@
   /**
    * {@inheritdoc}
    */
-  public function persist(Language $language) {
+  public function persist(LanguageInterface $language) {
     // Remember the method ID used to detect the language.
     $language->setNegotiationMethodId(static::METHOD_ID);
   }
diff -u b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationSession.php b/core/modules/language/lib/Drupal/language/Plugin/LanguageNegotiation/LanguageNegotiationSession.php
--- b/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 @@
   /**
    * {@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])) {
@@ -132,10 +132,10 @@
     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,
       );
only in patch2:
unchanged:
--- 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;
     $this->overrides = array();
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/PathProcessor/PathProcessorAlias.php
+++ b/core/lib/Drupal/Core/PathProcessor/PathProcessorAlias.php
@@ -45,7 +45,7 @@ public function processInbound($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 = $this->aliasManager->getPathAlias($path, $langcode);
     }
     return $path;
only in patch2:
unchanged:
--- 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;
 
 /**
@@ -260,14 +260,14 @@ 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.
only in patch2:
unchanged:
--- 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;
@@ -413,7 +414,7 @@ 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;
only in patch2:
unchanged:
--- 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);
 
 }
only in patch2:
unchanged:
--- 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.
only in patch2:
unchanged:
--- 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;
 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(LanguageInterface $language);
 
 }
only in patch2:
unchanged:
--- 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 = $target_user->getPreferredLangcode();
only in patch2:
unchanged:
--- a/core/modules/user/lib/Drupal/user/Entity/User.php
+++ b/core/modules/user/lib/Drupal/user/Entity/User.php
@@ -383,10 +383,10 @@ function getPreferredLangcode($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();
     }
   }
 
@@ -397,10 +397,10 @@ 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();
     }
   }