diff -u b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
--- b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
+++ b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\language;
 
-use Drupal\Core\Language\LanguageInterface;
+use Drupal\Core\Language\LanguageInterface as CoreLanguageInterface;
 use Drupal\Core\PhpStorage\PhpStorageFactory;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
@@ -136,7 +136,7 @@
    * {@inheritdoc}
    */
   public function isMultilingual() {
-    return count($this->getLanguages(LanguageInterface::STATE_CONFIGURABLE)) > 1;
+    return count($this->getLanguages(CoreLanguageInterface::STATE_CONFIGURABLE)) > 1;
   }
 
   /**
@@ -198,7 +198,7 @@
   /**
    * {@inheritdoc}
    */
-  public function getCurrentLanguage($type = LanguageInterface::TYPE_INTERFACE) {
+  public function getCurrentLanguage($type = CoreLanguageInterface::TYPE_INTERFACE) {
     if (!isset($this->negotiatedLanguages[$type])) {
       // Ensure we have a valid value for this language type.
       $this->negotiatedLanguages[$type] = $this->getDefaultLanguage();
@@ -215,8 +215,8 @@
         // original strings which can be translated by calling them again
         // afterwards. This can happen for instance while parsing negotiation
         // method definitions.
-        elseif ($type == LanguageInterface::TYPE_INTERFACE) {
-          return new Language(array('id' => LanguageInterface::LANGCODE_SYSTEM));
+        elseif ($type == CoreLanguageInterface::TYPE_INTERFACE) {
+          return new Language(array('id' => CoreLanguageInterface::LANGCODE_SYSTEM));
         }
       }
     }
@@ -270,7 +270,7 @@
   /**
    * {@inheritdoc}
    */
-  public function getLanguages($flags = LanguageInterface::STATE_CONFIGURABLE) {
+  public function getLanguages($flags = CoreLanguageInterface::STATE_CONFIGURABLE) {
     if (!isset($this->languages)) {
       // Prepopulate the language list with the default language to keep things
       // working even if we have no configuration.
@@ -311,15 +311,15 @@
     $max_weight = 0;
 
     // Get maximum weight to update the system languages to keep them on bottom.
-    foreach ($this->getLanguages(LanguageInterface::STATE_CONFIGURABLE) as $language) {
+    foreach ($this->getLanguages(CoreLanguageInterface::STATE_CONFIGURABLE) as $language) {
       if (!$language->isLocked() && $language->getWeight() > $max_weight) {
         $max_weight = $language->getWeight();
       }
     }
 
     // Loop locked languages to maintain the existing order.
-    $locked_languages = $this->getLanguages(LanguageInterface::STATE_LOCKED);
-    $config_ids = array_map(function(LanguageInterface $language) { return 'language.entity.' . $language->getId(); }, $locked_languages);
+    $locked_languages = $this->getLanguages(CoreLanguageInterface::STATE_LOCKED);
+    $config_ids = array_map(function(CoreLanguageInterface $language) { return 'language.entity.' . $language->getId(); }, $locked_languages);
     foreach ($this->configFactory->loadMultiple($config_ids) as $config_id => $config) {
       // Update system languages weight.
       $max_weight++;
@@ -336,7 +336,7 @@
       // Get languages ordered by weight, add LanguageInterface::LANGCODE_NOT_SPECIFIED
       // at the end.
       $candidates = array_keys($this->getLanguages());
-      $candidates[] = LanguageInterface::LANGCODE_NOT_SPECIFIED;
+      $candidates[] = CoreLanguageInterface::LANGCODE_NOT_SPECIFIED;
       $candidates = array_combine($candidates, $candidates);
 
       // The first candidate should always be the desired language if specified.
@@ -389,7 +389,7 @@
   /**
    * {@inheritdoc}
    */
-  public function setConfigOverrideLanguage(LanguageInterface $language = NULL) {
+  public function setConfigOverrideLanguage(CoreLanguageInterface $language = NULL) {
     $this->configFactoryOverride->setLanguage($language);
     return $this;
   }
diff -u b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodInterface.php b/core/modules/language/lib/Drupal/language/LanguageNegotiationMethodInterface.php
--- b/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\LanguageInterface;
+use Drupal\Core\Language\LanguageInterface as CoreLanguageInterface;
 use Drupal\Core\Session\AccountInterface;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -61,5 +61,5 @@
    *   The accepted language.
    */
-  public function persist(LanguageInterface $language);
+  public function persist(CoreLanguageInterface $language);
 
 }
diff -u b/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php b/core/modules/language/lib/Drupal/language/LanguageServiceProvider.php
--- b/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\LanguageInterface;
+use Drupal\Core\Language\LanguageInterface as CoreLanguageInterface;
 use Symfony\Component\DependencyInjection\Reference;
 
 /**
@@ -81,7 +81,7 @@
     //   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 . LanguageInterface::LANGCODE_NOT_SPECIFIED && $config_id != $prefix . LanguageInterface::LANGCODE_NOT_APPLICABLE;
+      return $config_id != $prefix . CoreLanguageInterface::LANGCODE_NOT_SPECIFIED && $config_id != $prefix . CoreLanguageInterface::LANGCODE_NOT_APPLICABLE;
     });
     return count($config_ids) > 1;
   }