diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index b00d23b..5a47d3b 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -9,7 +9,7 @@
 use Drupal\Core\Installer\Exception\AlreadyInstalledException;
 use Drupal\Core\Installer\Exception\InstallerException;
 use Drupal\Core\Installer\Exception\NoProfilesException;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\Core\Page\DefaultHtmlPageRenderer;
 use Drupal\Core\Site\Settings;
@@ -312,7 +312,7 @@ function install_begin_request(&$install_state) {
   // used or output for these calls.
   // @todo Separate API level checks from UI-facing error messages.
   $container = new ContainerBuilder();
-  $container->setParameter('language.default_values', Language::$defaultValues);
+  $container->setParameter('language.default_values', LanguageInterface::$defaultValues);
   $container
     ->register('language.default', 'Drupal\Core\Language\LanguageDefault')
     ->addArgument('%language.default_values%');
diff --git a/core/includes/update.inc b/core/includes/update.inc
index b54f572..910f3ff 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -839,7 +839,7 @@ function update_language_list($flags = LanguageInterface::STATE_CONFIGURABLE) {
           'weight' => $info['weight'],
         ));
       }
-      uasort($languages, '\Drupal\Core\Language\Language::sort');
+      uasort($languages, '\Drupal\Core\Language\LanguageInterface::sort');
     }
     else {
       // No language module, so use the default language only.
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index 9603d38..cbd344e 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -15,7 +15,7 @@
 use Drupal\Core\DependencyInjection\ServiceProviderInterface;
 use Drupal\Core\DependencyInjection\YamlFileLoader;
 use Drupal\Core\Extension\ExtensionDiscovery;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\Config\Loader\LoaderInterface;
 use Symfony\Component\DependencyInjection\ParameterBag\ParameterBag;
 use Symfony\Component\DependencyInjection\Dumper\PhpDumper;
@@ -533,7 +533,7 @@ class DrupalKernel implements DrupalKernelInterface, TerminableInterface {
     // avoids the circular dependencies that would created by
     // \Drupal\language\LanguageServiceProvider::alter() and allows the default
     // language to not be English in the installer.
-    $default_language_values = Language::$defaultValues;
+    $default_language_values = LanguageInterface::$defaultValues;
     if ($system = $this->getConfigStorage()->read('system.site')) {
       if ($default_language_values['id'] != $system['langcode']) {
         $default_language_values = array('id' => $system['langcode'], 'default' => TRUE);
diff --git a/core/modules/language/language.module b/core/modules/language/language.module
index beed875..ab6d5cc 100644
--- a/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -592,7 +592,7 @@ function language_modules_uninstalled($modules) {
  * Implements hook_ENTITY_TYPE_insert() for 'language_entity'.
  */
 function language_language_entity_insert(LanguageEntity $language) {
-  if (!empty($language->isLocked())) {
+  if (!$language->isLocked()) {
     return;
   }
 
diff --git a/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
index e34c126..9e938cb 100644
--- a/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
+++ b/core/modules/language/lib/Drupal/language/ConfigurableLanguageManager.php
@@ -1,4 +1,4 @@
-<?php
+ <?php
 
 /**
  * @file
@@ -298,7 +298,7 @@ class ConfigurableLanguageManager extends LanguageManager implements Configurabl
       $this->languages += $this->getDefaultLockedLanguages($weight);
 
       // Sort the language list by weight then title.
-      uasort($this->languages, '\Drupal\Core\Language\Language::sort');
+      uasort($this->languages, '\Drupal\Core\Language\LanguageInterface::sort');
     }
 
     return parent::getLanguages($flags);
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
index d6bd64f..a380e7f 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
@@ -10,7 +10,7 @@
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\KeyValueStore\KeyValueMemoryFactory;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\DependencyInjection\Reference;
 use Drupal\Core\Database\Database;
 use Symfony\Component\HttpFoundation\Request;
@@ -222,7 +222,7 @@ function __construct($test_id = NULL) {
     $this->container = $container;
 
     // Set the default language on the minimal container.
-    $this->container->setParameter('language.default_values', Language::$defaultValues);
+    $this->container->setParameter('language.default_values', LanguageInterface::$defaultValues);
 
     $container->register('lock', 'Drupal\Core\Lock\NullLockBackend');
     $container->register('cache_factory', 'Drupal\Core\Cache\MemoryBackendFactory');
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
index 19dd044..acdedc5 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -16,7 +16,7 @@
 use Drupal\Core\Database\ConnectionNotDefinedException;
 use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\DrupalKernel;
-use Drupal\Core\Language\Language;
+use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Session\AccountProxy;
 use Drupal\Core\Session\AnonymousUserSession;
 use Drupal\Core\Site\Settings;
@@ -1075,7 +1075,7 @@
     $this->container = new ContainerBuilder();
 
     // @todo Remove this once this class has no calls to t() and format_plural()
-    $this->container->setParameter('language.default_values', Language::$defaultValues);
+    $this->container->setParameter('language.default_values', LanguageInterface::$defaultValues);
     $this->container->register('language.default', 'Drupal\Core\Language\LanguageDefault')
       ->addArgument('%language.default_values%');
     $this->container->register('language_manager', 'Drupal\Core\Language\LanguageManager')
diff --git a/core/tests/Drupal/Tests/Core/Utility/TokenTest.php b/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
index 980ca93..9d08a26 100644
--- a/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
+++ b/core/tests/Drupal/Tests/Core/Utility/TokenTest.php
@@ -88,7 +88,7 @@ class TokenTest extends UnitTestCase {
 
     $this->languageManager->expects($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