diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index f189f95..7375004 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -16,6 +16,7 @@
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Language\LanguageManager;
+use Drupal\Core\Language\Language;
 use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
 
 /**
@@ -117,7 +118,7 @@ public function setCache(CacheBackendInterface $cache, LanguageManager $language
     $this->languageManager = $language_manager;
     $this->cache = $cache;
     $this->cacheKeyPrefix = $cache_key_prefix;
-    $this->cacheKey = $cache_key_prefix . ':' . $language_manager->getLanguage(LANGUAGE_TYPE_INTERFACE)->langcode;
+    $this->cacheKey = $cache_key_prefix . ':' . $language_manager->getLanguage(Language::TYPE_INTERFACE)->langcode;
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php b/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
index 6397640..9b8a421 100644
--- a/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
@@ -8,20 +8,8 @@
 namespace Drupal\Tests\Core\Plugin;
 
 use Drupal\Core\Language\Language;
-use Drupal\Core\Plugin\DefaultPluginManager;
 use Drupal\Tests\UnitTestCase;
 
-// @todo Remove once http://drupal.org/node/1620010 is committed.
-if (!defined('LANGUAGE_TYPE_INTERFACE')) {
-  define('LANGUAGE_TYPE_INTERFACE', 'language_interface');
-}
-if (!defined('LANGUAGE_LTR')) {
-  define('LANGUAGE_LTR', 0);
-}
-if (!defined('LANGUAGE_RTL')) {
-  define('LANGUAGE_RTL', 1);
-}
-
 /**
  * Tests the DefaultPluginManager.
  *
@@ -123,7 +111,7 @@ public function testDefaultPluginManagerWithEmptyCache() {
     $language_manager = $this->getMock('Drupal\Core\Language\LanguageManager');
     $language_manager->expects($this->once())
       ->method('getLanguage')
-      ->with(LANGUAGE_TYPE_INTERFACE)
+      ->with(Language::TYPE_INTERFACE)
       ->will($this->returnValue($language));
 
     $plugin_manager = new TestPluginManager($this->namespaces, $this->expectedDefinitions);
@@ -154,7 +142,7 @@ public function testDefaultPluginManagerWithFilledCache() {
     $language_manager = $this->getMock('Drupal\Core\Language\LanguageManager');
     $language_manager->expects($this->once())
       ->method('getLanguage')
-      ->with(LANGUAGE_TYPE_INTERFACE)
+      ->with(Language::TYPE_INTERFACE)
       ->will($this->returnValue($language));
 
     $plugin_manager = new TestPluginManager($this->namespaces, $this->expectedDefinitions);