diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index ac20992..4b1a45c 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;
@@ -1828,7 +1828,7 @@ function language($type) {
  * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
  *   Use \Drupal::languageManager()->getLanguages().
  */
-function language_list($flags = Language::STATE_CONFIGURABLE) {
+function language_list($flags = LanguageInterface::STATE_CONFIGURABLE) {
   return \Drupal::languageManager()->getLanguages($flags);
 }
 
@@ -1838,7 +1838,7 @@ function language_list($flags = Language::STATE_CONFIGURABLE) {
  * @param string $langcode
  *   The language code.
  *
- * @return \Drupal\core\Language\Language|null
+ * @return \Drupal\core\Language\LanguageInterface|null
  *   A fully-populated language object or NULL.
  *
  * @see \Drupal\Core\Language\LanguageManager::getLanguage()
@@ -1853,7 +1853,7 @@ function language_load($langcode) {
 /**
  * Returns the default language used on the site.
  *
- * @return \Drupal\Core\Language\Language
+ * @return \Drupal\Core\Language\LanguageInterface
  *   A language object.
  *
  * @see \Drupal\Core\Language\LanguageManager::getLanguage()
diff --git a/core/includes/common.inc b/core/includes/common.inc
index f30bcdf..26a3e69 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)->id;
 
   $output = "<channel>\n";
   $output .= ' <title>' . String::checkPlain($title) . "</title>\n";
@@ -1801,7 +1801,7 @@ function _drupal_add_js($data = NULL, $options = NULL) {
             'currentPath' => $current_path,
             'currentPathIsAdmin' => $current_path_is_admin,
             'isFront' => drupal_is_front_page(),
-            'currentLanguage' => \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_URL)->id,
+            'currentLanguage' => \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_URL)->id,
           );
           if (!empty($current_query)) {
             ksort($current_query);
diff --git a/core/lib/Drupal/Core/Config/ConfigModuleOverridesEvent.php b/core/lib/Drupal/Core/Config/ConfigModuleOverridesEvent.php
index 26692ea..a2c65d5 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;
 
 /**
@@ -33,7 +33,7 @@ class ConfigModuleOverridesEvent extends Event {
   /**
    * The Language object used to override configuration data.
    *
-   * @var \Drupal\Core\Language\Language
+   * @var \Drupal\Core\Language\LanguageInterface
    */
   protected $language;
 
@@ -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();
@@ -64,7 +64,7 @@ public function getNames() {
   /**
    * Gets configuration language.
    *
-   * @return \Drupal\Core\Language\Language
+   * @return \Drupal\Core\Language\LanguageInterface
    *   The configuration language object.
    */
   public function getLanguage() {
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
index 948ec6f..20bbcfc 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php
@@ -13,7 +13,7 @@
 use Drupal\Core\Entity\Entity;
 use Drupal\Core\Config\ConfigDuplicateUUIDException;
 use Drupal\Core\Entity\EntityStorageInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Plugin\PluginDependencyTrait;
 
 /**
@@ -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/Entity/ContentEntityBase.php b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
index 1895cfd..3eb0e02 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;
 
@@ -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] = $data;
         }
       }
@@ -429,12 +429,12 @@ protected function getTranslatedField($name, $langcode) {
       // Non-translatable fields are always stored with
       // Language::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];
     }
@@ -576,25 +576,22 @@ protected function setDefaultLangcode() {
     }
     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);
     }
   }
 
   /**
    * Updates language for already instantiated fields.
-   *
-   * @return \Drupal\Core\Language\Language
-   *   A language object.
    */
   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 +627,8 @@ 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 +671,7 @@ public function getTranslation($langcode) {
    * {@inheritdoc}
    */
   public function getUntranslated() {
-    return $this->getTranslation(Language::LANGCODE_DEFAULT);
+    return $this->getTranslation(LanguageInterface::LANGCODE_DEFAULT);
   }
 
   /**
@@ -721,7 +718,7 @@ protected function initializeTranslation($langcode) {
    */
   public function hasTranslation($langcode) {
     if ($langcode == $this->defaultLangcode) {
-      $langcode = Language::LANGCODE_DEFAULT;
+      $langcode = LanguageInterface::LANGCODE_DEFAULT;
     }
     return !empty($this->translations[$langcode]['status']);
   }
@@ -766,7 +763,7 @@ public function addTranslation($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][$langcode]);
@@ -785,7 +782,7 @@ public function removeTranslation($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 +792,7 @@ 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 +954,7 @@ 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 2214894..f42c091 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityDatabaseStorage.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Database\Connection;
 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 +163,12 @@ 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] = $value;
         }
       }
       // If we have no multilingual values we can instantiate entity objecs
@@ -209,7 +209,7 @@ protected function attachPropertyData(array &$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, $revision_ids);
       }
@@ -229,7 +229,7 @@ protected function attachPropertyData(array &$entities) {
 
         // Field values in default language are stored with
         // Language::LANGCODE_DEFAULT as key.
-        $langcode = empty($values['default_langcode']) ? $values['langcode'] : Language::LANGCODE_DEFAULT;
+        $langcode = empty($values['default_langcode']) ? $values['langcode'] : LanguageInterface::LANGCODE_DEFAULT;
         $translations[$id][$langcode] = TRUE;
 
         foreach (array_keys($field_definitions) as $field_name) {
@@ -255,7 +255,7 @@ protected function attachPropertyData(array &$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[$id]));
       }
@@ -738,7 +738,7 @@ protected function doLoadFieldItems($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);
 
diff --git a/core/lib/Drupal/Core/Entity/Entity.php b/core/lib/Drupal/Core/Entity/Entity.php
index b69ba1d..9a09c99 100644
--- a/core/lib/Drupal/Core/Entity/Entity.php
+++ b/core/lib/Drupal/Core/Entity/Entity.php
@@ -17,6 +17,7 @@
 use Drupal\Core\Entity\Exception\NoCorrespondingEntityClassException;
 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;
 
@@ -283,7 +284,7 @@ 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);
   }
 
   /**
@@ -293,7 +294,7 @@ 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..afab887 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;
 
 /**
@@ -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/EntityInterface.php b/core/lib/Drupal/Core/Entity/EntityInterface.php
index 4e483df..e43c3ae 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..5587c33 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;
@@ -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)->id;
       }
 
       // 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->id] = 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 = $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_INTERFACE)->id;
       if ($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..71d3308 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)->id;
     }
 
     $build_list = array(
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/LanguageDefault.php b/core/lib/Drupal/Core/Language/LanguageDefault.php
index a72b8b1..1ca8009 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() {
@@ -49,10 +49,10 @@ 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) {
+  public function set(LanguageInterface $language) {
     $language->default = TRUE;
     $this->language = $language;
   }
diff --git a/core/lib/Drupal/Core/Language/LanguageManager.php b/core/lib/Drupal/Core/Language/LanguageManager.php
index 3d943d0..d596853 100644
--- a/core/lib/Drupal/Core/Language/LanguageManager.php
+++ b/core/lib/Drupal/Core/Language/LanguageManager.php
@@ -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();
   }
 
@@ -107,7 +107,7 @@ public function getDefaultLanguage() {
   /**
    * {@inheritdoc}
    */
-  public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
+  public function getLanguages($flags = LanguageInterface::STATE_CONFIGURABLE) {
     // Initialize master language list.
     if (!isset($this->languages)) {
       // No language module, so use the default language only.
@@ -123,7 +123,7 @@ public function getLanguages($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' => $default->name));
@@ -131,7 +131,7 @@ public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
     }
 
     foreach ($this->languages as $id => $language) {
-      if (($language->locked && ($flags & Language::STATE_LOCKED)) || (!$language->locked && ($flags & Language::STATE_CONFIGURABLE))) {
+      if (($language->locked && ($flags & LanguageInterface::STATE_LOCKED)) || (!$language->locked && ($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;
   }
 
@@ -151,7 +151,7 @@ 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)) {
@@ -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,
     ) + $locked_language);
@@ -200,7 +200,7 @@ public function isLanguageLocked($langcode) {
    * {@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..2869f3c 100644
--- a/core/lib/Drupal/Core/Language/LanguageManagerInterface.php
+++ b/core/lib/Drupal/Core/Language/LanguageManagerInterface.php
@@ -50,10 +50,10 @@ public function getLanguageTypes();
    *   (optional) The language type, e.g. the interface or the content language.
    *   Defaults to \Drupal\Core\Language\Language::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.
@@ -71,7 +71,7 @@ public function reset($type = NULL);
   /**
    * Returns a language object representing the site's default language.
    *
-   * @return \Drupal\Core\Language\Language
+   * @return \Drupal\Core\Language\LanguageInterface
    *   A language object.
    */
   public function getDefaultLanguage();
@@ -87,7 +87,7 @@ public function getDefaultLanguage();
    * @return array
    *   An associative array of languages, keyed by the language code.
    */
-  public function getLanguages($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 $language
    *   The current configuration override language.
    */
   public function getConfigOverrideLanguage();
diff --git a/core/lib/Drupal/Core/Path/AliasManager.php b/core/lib/Drupal/Core/Path/AliasManager.php
index 55d2ddc..645e3b6 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)->id;
 
     // 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)->id;
 
     // 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/Utility/Token.php b/core/lib/Drupal/Core/Utility/Token.php
index 4a1238e..d03d645 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)->id;
       $cache = $this->cache->get($cache_id);
       if ($cache) {
         $this->tokenInfo = $cache->data;
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedForm.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedForm.php
index 1770f03..d13274f 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;
 
 /**
@@ -31,7 +31,7 @@ public function form(array $form, array &$form_state) {
       '#title' => $this->t('Language'),
       '#type' => 'language_select',
       '#default_value' => $feed->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#languages' => LanguageInterface::STATE_ALL,
       '#weight' => -4,
     );
 
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..aa668d8 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;
 
@@ -110,7 +110,7 @@ public function form(array $form, array &$form_state) {
       '#title' => $this->t('Language'),
       '#type' => 'language_select',
       '#default_value' => $block->getUntranslated()->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#languages' => LanguageInterface::STATE_ALL,
       '#access' => isset($language_configuration['language_show']) && $language_configuration['language_show'],
     );
 
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 1249dab..866f1b8 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;
@@ -157,7 +157,7 @@ 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 $language->name is not wrapped with t(), it should be replaced
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index 9cc4835..5f11fba 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -11,7 +11,7 @@
 use Drupal\Core\Render\Element;
 use Drupal\node\NodeInterface;
 use Drupal\node\NodeTypeInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
 use Drupal\Core\Template\Attribute;
 use Symfony\Component\HttpFoundation\Request;
@@ -491,7 +491,7 @@ function template_preprocess_book_export_html(&$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->direction == LanguageInterface::DIRECTION_RTL);
   $variables['head'] = drupal_get_html_head();
 
   // HTML element attributes.
diff --git a/core/modules/comment/lib/Drupal/comment/CommentForm.php b/core/modules/comment/lib/Drupal/comment/CommentForm.php
index 6fd7ff6..1e9a241 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;
 
@@ -64,7 +64,7 @@ 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);
+      $language_content = \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
       $comment->langcode->value = $language_content->id;
     }
 
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/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/Form/ConfigTranslationFormBase.php b/core/modules/config_translation/lib/Drupal/config_translation/Form/ConfigTranslationFormBase.php
index fb3ba88..1ff96bb 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;
@@ -71,7 +71,7 @@
   /**
    * The language of the configuration translation.
    *
-   * @var \Drupal\Core\Language\Language
+   * @var \Drupal\Core\Language\LanguageInterface
    */
   protected $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.
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..18b9666 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'));
     }
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..63aecf3 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;
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..44105ba 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;
 
 /**
@@ -19,7 +19,7 @@ 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,
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..ced73ab 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;
 
 /**
@@ -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/content_translation/content_translation.admin.inc b/core/modules/content_translation/content_translation.admin.inc
index eb03aea..d2a3e1e 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;
@@ -278,7 +278,7 @@ 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) {
+          foreach (\Drupal::languageManager()->getLanguages(LanguageInterface::STATE_LOCKED) as $language) {
             $locked_languages[] = $language->name;
           }
           form_set_error($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 $name) {
diff --git a/core/modules/content_translation/content_translation.module b/core/modules/content_translation/content_translation.module
index 502d4e4..d7c95db 100644
--- a/core/modules/content_translation/content_translation.module
+++ b/core/modules/content_translation/content_translation.module
@@ -11,7 +11,7 @@
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Field\FieldDefinition;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\TypedData\TranslatableInterface;
 use Drupal\field\Entity\FieldInstanceConfig;
@@ -72,8 +72,8 @@ function content_translation_module_implements_alter(&$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']);
 }
 
 /**
@@ -792,7 +792,7 @@ 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) {
+    foreach (\Drupal::languageManager()->getLanguages(LanguageInterface::STATE_LOCKED) as $language) {
       $locked_languages[] = $language->name;
     }
     // @todo Set the correct form element name as soon as the element parents
diff --git a/core/modules/content_translation/content_translation.pages.inc b/core/modules/content_translation/content_translation.pages.inc
index d4a7c48..9898678 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;
 
@@ -171,12 +171,12 @@ 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 LanguageInterface::TYPE_CONTENT,
+    // ergo we also need to use interface switch links.
+    $links = \Drupal::languageManager()->getLanguageSwitchLinks(LanguageInterface::TYPE_INTERFACE, $path);
   }
   return $links;
 }
@@ -186,10 +186,10 @@ function _content_translation_get_switch_links($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 $target
  *   (optional) The language of the translated values. Defaults to the current
  *   content language.
  *
@@ -199,9 +199,9 @@ function _content_translation_get_switch_links($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;
@@ -216,7 +216,7 @@ 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.
  *
@@ -226,8 +226,8 @@ 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);
+function content_translation_edit_page(EntityInterface $entity, LanguageInterface $language = NULL) {
+  $language = !empty($language) ? $language : \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
   $form_state['langcode'] = $language->id;
   $form_state['content_translation']['translation_form'] = TRUE;
   return \Drupal::service('entity.form_builder')->getForm($entity, 'default', $form_state);
@@ -238,12 +238,12 @@ 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());
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..137b52e 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;
@@ -70,7 +70,7 @@ 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);
+          $target = language_load($target) ?: \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
           return ($source->id != $target->id
             && isset($languages[$source->id])
             && isset($languages[$target->id])
@@ -80,7 +80,7 @@ public function access(Route $route, Request $request, AccountInterface $account
 
         case 'update':
         case 'delete':
-          $language = language_load($language) ?: \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT);
+          $language = language_load($language) ?: \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
           return isset($languages[$language->id])
             && $language->id != $entity->getUntranslated()->language()->id
             && isset($translations[$language->id])
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..bd9a9c1 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;
 
 /**
@@ -129,7 +129,7 @@ public function entityFormAlter(array &$form, array &$form_state, EntityInterfac
           '#submit' => array(array($this, 'entityFormSourceChange')),
         ),
       );
-      foreach (language_list(Language::STATE_CONFIGURABLE) as $language) {
+      foreach (language_list(LanguageInterface::STATE_CONFIGURABLE) as $language) {
         if (isset($translations[$language->id])) {
           $form['source_langcode']['source']['#options'][$language->id] = $language->name;
         }
@@ -142,7 +142,7 @@ public function entityFormAlter(array &$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) {
+      foreach (language_list(LanguageInterface::STATE_CONFIGURABLE) as $language) {
         if (empty($translations[$language->id]) || $language->id == $entity_langcode) {
           $form['langcode']['#options'][$language->id] = $language->name;
         }
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..d03d30c 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
@@ -7,7 +7,7 @@
 
 namespace Drupal\content_translation\Tests;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\simpletest\WebTestBase;
 
@@ -76,7 +76,7 @@ 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/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/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/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/Plugin/views/field/Field.php b/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
index 84b587a..e7f9e01 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;
@@ -295,7 +295,7 @@ public function query($use_groupby = FALSE) {
         $default_langcode = language_default()->id;
         $langcode = str_replace(
           array('***CURRENT_LANGUAGE***', '***DEFAULT_LANGUAGE***'),
-          array($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();
@@ -903,7 +903,7 @@ function field_langcode(EntityInterface $entity) {
       $default_langcode = language_default()->id;
       $langcode = str_replace(
         array('***CURRENT_LANGUAGE***', '***DEFAULT_LANGUAGE***'),
-        array($this->languageManager->getCurrentLanguage(Language::TYPE_CONTENT), $default_langcode),
+        array($this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT), $default_langcode),
         $this->view->display_handler->options['field_language']
       );
 
@@ -917,7 +917,7 @@ function field_langcode(EntityInterface $entity) {
       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/FieldTestBase.php b/core/modules/field/lib/Drupal/field/Tests/FieldTestBase.php
index 3f5d2c5..6bf45a4 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..9f250d2 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_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/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/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/language/language.module b/core/modules/language/language.module
index f35da4d..8ca2c13 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;
   }
 }
@@ -214,7 +214,7 @@ function language_configuration_element_default_options() {
     '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)) : $language->name;
   }
@@ -460,7 +460,7 @@ function language_save($language) {
  *   TRUE if language is successfully deleted. Otherwise FALSE.
  */
 function language_delete($langcode) {
-  $languages = \Drupal::languageManager()->getLanguages(Language::STATE_ALL);
+  $languages = \Drupal::languageManager()->getLanguages(LanguageInterface::STATE_ALL);
   if (isset($languages[$langcode]) && !$languages[$langcode]->locked) {
     $language = $languages[$langcode];
 
@@ -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,
     ),
diff --git a/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
index bfadec0..cc37081 100644
--- a/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
+++ b/core/modules/language/lib/Drupal/language/Config/LanguageConfigFactoryOverride.php
@@ -10,8 +10,8 @@
 use Drupal\Core\Config\Config;
 use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\Config\TypedConfigManagerInterface;
-use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageDefault;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 
 /**
@@ -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..fad871f 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 BaseLanguageInterface;
 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(BaseLanguageInterface::STATE_CONFIGURABLE)) > 1;
   }
 
   /**
@@ -197,7 +198,7 @@ public function saveLanguageTypesConfiguration(array $values) {
   /**
    * {@inheritdoc}
    */
-  public function getCurrentLanguage($type = Language::TYPE_INTERFACE) {
+  public function getCurrentLanguage($type = BaseLanguageInterface::TYPE_INTERFACE) {
     if (!isset($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 == BaseLanguageInterface::TYPE_INTERFACE) {
+          return new Language(array('id' => BaseLanguageInterface::LANGCODE_SYSTEM));
         }
       }
     }
@@ -269,7 +270,7 @@ public function setNegotiator(LanguageNegotiatorInterface $negotiator) {
   /**
    * {@inheritdoc}
    */
-  public function getLanguages($flags = Language::STATE_CONFIGURABLE) {
+  public function getLanguages($flags = BaseLanguageInterface::STATE_CONFIGURABLE) {
     if (!isset($this->languages)) {
       // Prepopulate the language list with the default language to keep things
       // working even if we have no configuration.
@@ -310,14 +311,14 @@ 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 $language) {
+    foreach ($this->getLanguages(BaseLanguageInterface::STATE_CONFIGURABLE) as $language) {
       if (!$language->locked && $language->weight > $max_weight) {
         $max_weight = $language->weight;
       }
     }
 
     // Loop locked languages to maintain the existing order.
-    $locked_languages = $this->getLanguages(Language::STATE_LOCKED);
+    $locked_languages = $this->getLanguages(BaseLanguageInterface::STATE_LOCKED);
     $config_ids = array_map(function($language) { return 'language.entity.' . $language->id; }, $locked_languages);
     foreach ($this->configFactory->loadMultiple($config_ids) as $config_id => $config) {
       // Update system languages weight.
@@ -335,7 +336,7 @@ public function getFallbackCandidates($langcode = NULL, array $context = array()
       // Get languages ordered by weight, add Language::LANGCODE_NOT_SPECIFIED
       // at the end.
       $candidates = array_keys($this->getLanguages());
-      $candidates[] = Language::LANGCODE_NOT_SPECIFIED;
+      $candidates[] = BaseLanguageInterface::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(BaseLanguageInterface $language = NULL) {
     $this->configFactoryOverride->setLanguage($language);
     return $this;
   }
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/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/LanguageNegotiationMethodBase.php b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodBase.php
index 9ed0f7c..3f48f7a 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 BaseLanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 
 /**
@@ -61,7 +61,7 @@ public function setCurrentUser(AccountInterface $current_user) {
   /**
    * {@inheritdoc}
    */
-  public function persist(Language $language) {
+  public function persist(BaseLanguageInterface $language) {
     // Remember the method ID used to detect the language.
     $language->method_id = 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..1913d41 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 BaseLanguageInterface;
 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(BaseLanguageInterface $language);
 
 }
diff --git a/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php b/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php
index 95eb700..a565c1c 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 BaseLanguageInterface;
 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 . BaseLanguageInterface::LANGCODE_NOT_SPECIFIED && $config_id != $prefix . BaseLanguageInterface::LANGCODE_NOT_APPLICABLE;
     });
     return count($config_ids) > 1;
   }
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..8cf294a 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;
@@ -68,7 +68,7 @@ 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
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..18a2805 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;
@@ -129,7 +129,7 @@ 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.
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageConfigurationTest.php
index 6093263..39eb36f 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;
 
 /**
@@ -160,7 +160,7 @@ 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) {
+    foreach (\Drupal::languageManager()->getLanguages(LanguageInterface::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));
     }
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php
index 9554dd8..b8481ac 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageCustomLanguageConfigurationTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Functional tests for language configuration.
@@ -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/LanguageFallbackTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageFallbackTest.php
index fb621d8..335909b 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.
@@ -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.
@@ -57,8 +58,8 @@ 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.');
 
@@ -70,7 +71,7 @@ public function testCandidates() {
       }
     }
     $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..6d45905 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Functional tests for the language list configuration forms.
@@ -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..19d4d82 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;
 
@@ -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/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..9ccdd9f 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageUILanguageNegotiationTest.php
@@ -14,6 +14,7 @@
 use Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Drupal\language\LanguageNegotiatorInterface;
 
@@ -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
diff --git a/core/modules/language/tests/language_test/language_test.module b/core/modules/language/tests/language_test/language_test.module
index e1fd47e..aaa34fd 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;
 
 /**
@@ -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
-    // configurable.
+    $language_types[LanguageInterface::TYPE_CONTENT]['locked'] = FALSE;
+    unset($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', $configurable)->save();
     }
   }
@@ -80,7 +80,7 @@ function language_test_store_language_negotiation() {
  */
 function language_test_language_fallback_candidates_alter(array &$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/locale/lib/Drupal/locale/Form/ExportForm.php b/core/modules/locale/lib/Drupal/locale/Form/ExportForm.php
index 433c8c9..189947e 100644
--- a/core/modules/locale/lib/Drupal/locale/Form/ExportForm.php
+++ b/core/modules/locale/lib/Drupal/locale/Form/ExportForm.php
@@ -10,6 +10,7 @@
 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;
@@ -69,7 +70,7 @@ 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',
@@ -84,7 +85,7 @@ public function buildForm(array $form, array &$form_state) {
         '#options' => $language_options,
         '#default_value' => $language_default->id,
         '#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 +94,7 @@ 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 +130,7 @@ 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 {
diff --git a/core/modules/locale/lib/Drupal/locale/LocaleConfigManager.php b/core/modules/locale/lib/Drupal/locale/LocaleConfigManager.php
index 3c0dc57..a48a895 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;
 
@@ -308,13 +308,13 @@ 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 $language) {
+  public function hasTranslation($name, LanguageInterface $language) {
     $translation = $this->languageManager->getLanguageConfigOverride($language->id, $name);
     return !$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/Tests/LocalePathTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocalePathTest.php
index cae7f4b..64d9b1b 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');
@@ -118,7 +118,7 @@ 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(
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
index fa33010..ed3660d 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleTranslationUiTest.php
@@ -10,6 +10,7 @@
 use Drupal\Core\Cache\Cache;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 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 Language::LANGCODE_SYSTEM.');
 
     $search = array(
       'string' => $name,
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index 06c0887..2aafd92 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -7,6 +7,7 @@
 
 use Drupal\locale\Gettext;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\file\FileInterface;
 
 /**
@@ -192,7 +193,7 @@ 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($context['sandbox'])) {
@@ -459,7 +460,7 @@ function locale_translate_file_attach_properties($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 $file;
 }
diff --git a/core/modules/locale/locale.module b/core/modules/locale/locale.module
index d3e05dc..06fa802 100644
--- a/core/modules/locale/locale.module
+++ b/core/modules/locale/locale.module
@@ -15,6 +15,7 @@
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Entity\Language as LanguageEntity;
 use Drupal\Component\Utility\Crypt;
 use Symfony\Component\HttpFoundation\Request;
@@ -628,7 +629,7 @@ function locale_library_alter(array &$library, $name) {
 
     $language_interface = \Drupal::languageManager()->getCurrentLanguage();
     $settings['jquery']['ui']['datepicker'] = array(
-      'isRTL' => $language_interface->direction == Language::DIRECTION_RTL,
+      'isRTL' => $language_interface->direction == LanguageInterface::DIRECTION_RTL,
       'firstDay' => \Drupal::config('system.date')->get('first_day'),
     );
     $library['js'][] = array(
@@ -801,7 +802,7 @@ function locale_system_file_system_settings_submit(&$form, $form_state) {
  * Implements hook_preprocess_HOOK() for node templates.
  */
 function locale_preprocess_node(&$variables) {
-  if ($variables['node']->language()->id != Language::LANGCODE_NOT_SPECIFIED) {
+  if ($variables['node']->language()->id != LanguageInterface::LANGCODE_NOT_SPECIFIED) {
     $language_interface = \Drupal::languageManager()->getCurrentLanguage();
 
     $node_language = $variables['node']->language();
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 4913b83..b24ae13 100644
--- a/core/modules/menu_ui/lib/Drupal/menu_ui/MenuForm.php
+++ b/core/modules/menu_ui/lib/Drupal/menu_ui/MenuForm.php
@@ -11,6 +11,7 @@
 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 +118,7 @@ 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/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..6b57800 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()->id, 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..520dccf 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()->id, 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..8c7d939 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()->id);
 
     $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..128dc3c 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()->id);
     $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()->id);
     $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/Entity/Node.php b/core/modules/node/lib/Drupal/node/Entity/Node.php
index 1d21504..44042d4 100644
--- a/core/modules/node/lib/Drupal/node/Entity/Node.php
+++ b/core/modules/node/lib/Drupal/node/Entity/Node.php
@@ -12,6 +12,7 @@
 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;
@@ -163,7 +164,7 @@ public function prepareLangcode() {
       // 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;
+      $content_negotiation_langcode = \Drupal::languageManager()->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->id;
       // If there is a translation available, use it.
       if (isset($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..18a3c4b 100644
--- a/core/modules/node/lib/Drupal/node/NodeAccessController.php
+++ b/core/modules/node/lib/Drupal/node/NodeAccessController.php
@@ -12,6 +12,7 @@
 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 +59,7 @@ 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..6a8c193 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;
 
 /**
@@ -90,7 +90,7 @@ public function form(array $form, array &$form_state) {
       '#title' => t('Language'),
       '#type' => 'language_select',
       '#default_value' => $node->getUntranslated()->language()->id,
-      '#languages' => Language::STATE_ALL,
+      '#languages' => LanguageInterface::STATE_ALL,
       '#access' => isset($language_configuration['language_show']) && $language_configuration['language_show'],
     );
 
diff --git a/core/modules/node/lib/Drupal/node/NodeStorage.php b/core/modules/node/lib/Drupal/node/NodeStorage.php
index 8bb17fd..55a660c 100644
--- a/core/modules/node/lib/Drupal/node/NodeStorage.php
+++ b/core/modules/node/lib/Drupal/node/NodeStorage.php
@@ -11,6 +11,7 @@
 use Drupal\Core\Entity\ContentEntityDatabaseStorage;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 
 /**
  * Defines the controller class for nodes.
@@ -55,7 +56,7 @@ public function updateType($old_type, $new_type) {
    */
   public function clearRevisionsLanguage($language) {
     return $this->database->update('node_revision')
-      ->fields(array('langcode' => Language::LANGCODE_NOT_SPECIFIED))
+      ->fields(array('langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED))
       ->condition('langcode', $language->id)
       ->execute();
   }
diff --git a/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php b/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php
index 1bcd79b..ecb01d6 100644
--- a/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php
+++ b/core/modules/node/lib/Drupal/node/Plugin/Search/NodeSearch.php
@@ -13,7 +13,7 @@
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\State\StateInterface;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Access\AccessibleInterface;
 use Drupal\Core\Database\Query\Condition;
@@ -452,7 +452,7 @@ public function searchFormAlter(array &$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;
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeAccessLanguageTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeAccessLanguageTest.php
index feeae45..5eec5d9 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.
@@ -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()->id == 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);
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..9bd8253 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeFieldMultilingualTestCase.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeFieldMultilingualTestCase.php
@@ -101,7 +101,7 @@ function testMultilingualNodeForm() {
     $this->assertTrue($node->language()->id == $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/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/node.module b/core/modules/node/node.module
index 2253f71..dd2eb56 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -10,6 +10,7 @@
 
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\Request;
@@ -1033,7 +1034,7 @@ 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(LanguageInterface::TYPE_CONTENT);
   $rss_config = \Drupal::config('system.rss');
 
   if ($nids === FALSE) {
diff --git a/core/modules/node/node.tokens.inc b/core/modules/node/node.tokens.inc
index 8789047..6a09163 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']);
 
diff --git a/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
index 100ad29..114dcca 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;
 
@@ -896,7 +897,7 @@ public function testGetTranslationFromContext() {
     $entity->expects($this->exactly(2))
       ->method('hasTranslation')
       ->will($this->returnValueMap(array(
-        array(Language::LANGCODE_DEFAULT, FALSE),
+        array(LanguageInterface::LANGCODE_DEFAULT, FALSE),
         array('custom_langcode', TRUE),
       )));
 
diff --git a/core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php b/core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php
index f58edc5..bdcd093 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;
@@ -78,7 +78,7 @@ 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..2f67a7b 100644
--- a/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
+++ b/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\Tests\Core\Utility;
 
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Utility\Token;
 use Drupal\Tests\UnitTestCase;
 
@@ -87,7 +87,7 @@ public function testGetInfo() {
 
     $this->languageManager->expects($this->once())
       ->method('getCurrentLanguage')
-      ->with(Language::TYPE_CONTENT)
+      ->with(LanguageInterface::TYPE_CONTENT)
       ->will($this->returnValue($language));
 
     // The persistent cache must only be hit once, after which the info is