diff --git a/core/modules/ckeditor/src/Tests/CKEditorTest.php b/core/modules/ckeditor/src/Tests/CKEditorTest.php
index caf0345..02dc2f4 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -383,6 +383,7 @@ function testLanguages() {
    */
   function testJSTranslation() {
     $this->enableModules(array('language', 'locale'));
+    $this->installConfig(['language']);
     $this->installSchema('locale', 'locales_source');
     $this->installSchema('locale', 'locales_location');
     $this->installSchema('locale', 'locales_target');
diff --git a/core/modules/config/src/Tests/ConfigLanguageOverrideTest.php b/core/modules/config/src/Tests/ConfigLanguageOverrideTest.php
index b96819e..1b07239 100644
--- a/core/modules/config/src/Tests/ConfigLanguageOverrideTest.php
+++ b/core/modules/config/src/Tests/ConfigLanguageOverrideTest.php
@@ -29,7 +29,7 @@ class ConfigLanguageOverrideTest extends KernelTestBase {
    */
   protected function setUp() {
     parent::setUp();
-    $this->installConfig(array('config_test'));
+    $this->installConfig(array('config_test', 'language'));
   }
 
   /**
diff --git a/core/modules/language/src/Entity/ConfigurableLanguage.php b/core/modules/language/src/Entity/ConfigurableLanguage.php
index a754654..d029714 100644
--- a/core/modules/language/src/Entity/ConfigurableLanguage.php
+++ b/core/modules/language/src/Entity/ConfigurableLanguage.php
@@ -121,6 +121,17 @@ public function preSave(EntityStorageInterface $storage) {
     // For the uncommon case of custom languages the label should be given in
     // English.
     $this->langcode = 'en';
+
+    // When adding a new language the weight shouldn't be zero to avoid a
+    // reordering of the languages list when their names change i.e. interface
+    // translation. The english language is special cased because it is provided
+    // as default configuration with a valid weight of 0.
+    if ($this->id != 'en' && $this->isNew() && !$this->isLocked() && $this->getWeight() == 0) {
+      // Fetch all configurable languages ordered by weight.
+      $languages = \Drupal::languageManager()->getLanguages($this::STATE_CONFIGURABLE);
+      $last_language = end($languages);
+      $this->setWeight($last_language->getWeight() + 1);
+    }
   }
 
   /**
@@ -131,7 +142,7 @@ public function postSave(EntityStorageInterface $storage, $update = TRUE) {
 
     $language_manager = \Drupal::languageManager();
     $language_manager->reset();
-    if (!$this->isLocked() && $language_manager instanceof ConfigurableLanguageManagerInterface) {
+    if (!$this->isLocked() && $language_manager instanceof ConfigurableLanguageManagerInterface && !$this->isSyncing()) {
       $language_manager->updateLockedLanguageWeights();
     }
 
@@ -173,7 +184,8 @@ public static function postDelete(EntityStorageInterface $storage, array $entiti
     parent::postDelete($storage, $entities);
     $language_manager = \Drupal::languageManager();
     $language_manager->reset();
-    if ($language_manager instanceof ConfigurableLanguageManagerInterface) {
+    $entity = reset($entities);
+    if ($language_manager instanceof ConfigurableLanguageManagerInterface && !$entity->isUninstalling() && !$entity->isSyncing()) {
       $language_manager->updateLockedLanguageWeights();
     }
     // If after deleting this language the site will become monolingual, we need
diff --git a/core/modules/language/src/Tests/EntityDefaultLanguageTest.php b/core/modules/language/src/Tests/EntityDefaultLanguageTest.php
index b3b109a..0878cad 100644
--- a/core/modules/language/src/Tests/EntityDefaultLanguageTest.php
+++ b/core/modules/language/src/Tests/EntityDefaultLanguageTest.php
@@ -30,7 +30,7 @@ class EntityDefaultLanguageTest extends KernelTestBase {
    */
   public function setUp() {
     parent::setUp();
-
+    $this->installConfig(['language']);
     $this->installEntitySchema('user');
 
     // Activate Spanish language, so there are two languages activated.
diff --git a/core/modules/language/src/Tests/LanguageConfigOverrideInstallTest.php b/core/modules/language/src/Tests/LanguageConfigOverrideInstallTest.php
index 0364079..9392301 100644
--- a/core/modules/language/src/Tests/LanguageConfigOverrideInstallTest.php
+++ b/core/modules/language/src/Tests/LanguageConfigOverrideInstallTest.php
@@ -24,6 +24,14 @@ class LanguageConfigOverrideInstallTest extends KernelTestBase {
   public static $modules = array('language', 'config_events_test');
 
   /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+    $this->installConfig(['language']);
+  }
+
+  /**
    * Tests the configuration events are not fired during install of overrides.
    */
   public function testLanguageConfigOverrideInstall() {
diff --git a/core/modules/language/src/Tests/LanguageListTest.php b/core/modules/language/src/Tests/LanguageListTest.php
index 8ec846c..22a638f 100644
--- a/core/modules/language/src/Tests/LanguageListTest.php
+++ b/core/modules/language/src/Tests/LanguageListTest.php
@@ -35,6 +35,10 @@ function testLanguageList() {
     $admin_user = $this->drupalCreateUser(array('administer languages', 'access administration pages'));
     $this->drupalLogin($admin_user);
 
+    // Get the weight of the last language.
+    $languages = \Drupal::service('language_manager')->getLanguages();
+    $last_language_weight = end($languages)->getWeight();
+
     // Add predefined language.
     $edit = array(
       'predefined_langcode' => 'fr',
@@ -43,6 +47,14 @@ function testLanguageList() {
     $this->assertText('French', 'Language added successfully.');
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]));
 
+    // Get the weight of the last language and check that the weight is one unit
+    // heavier and than the last configurable language.
+    $this->rebuildContainer();
+    $languages = \Drupal::service('language_manager')->getLanguages();
+    $last_language = end($languages);
+    $this->assertEqual($last_language->getWeight(), $last_language_weight + 1);
+    $this->assertEqual($last_language->getId(), $edit['predefined_langcode']);
+
     // Add custom language.
     $langcode = 'xx';
     $name = $this->randomMachineName(16);
diff --git a/core/modules/locale/src/Tests/LocaleConfigManagerTest.php b/core/modules/locale/src/Tests/LocaleConfigManagerTest.php
index 4cc9fb2..299f366 100644
--- a/core/modules/locale/src/Tests/LocaleConfigManagerTest.php
+++ b/core/modules/locale/src/Tests/LocaleConfigManagerTest.php
@@ -29,7 +29,7 @@ class LocaleConfigManagerTest extends KernelTestBase {
    */
   public function testHasTranslation() {
     $this->installSchema('locale', array('locales_location'));
-    $this->installConfig(array('locale_test'));
+    $this->installConfig(array('locale_test', 'language'));
     $locale_config_manager = \Drupal::service('locale.config.typed');
 
     $language = ConfigurableLanguage::createFromLangcode('de');
diff --git a/core/modules/locale/src/Tests/LocaleConfigSubscriberTest.php b/core/modules/locale/src/Tests/LocaleConfigSubscriberTest.php
index f3f7415..40fea1a 100644
--- a/core/modules/locale/src/Tests/LocaleConfigSubscriberTest.php
+++ b/core/modules/locale/src/Tests/LocaleConfigSubscriberTest.php
@@ -72,7 +72,7 @@ protected function setUp() {
 
     $this->installSchema('locale', ['locales_source', 'locales_target', 'locales_location']);
 
-    $this->installConfig(['locale_test']);
+    $this->installConfig(['locale_test', 'language']);
     ConfigurableLanguage::createFromLangcode($this->langcode)->save();
   }
 
diff --git a/core/modules/system/src/Tests/Entity/EntityTranslationTest.php b/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
index 2e8a3b3..98362a7 100644
--- a/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
+++ b/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
@@ -504,7 +504,8 @@ protected function doTestLanguageFallback($entity_type) {
     $langcode_key = $this->entityManager->getDefinition($entity_type)->getKey('langcode');
     $languages = $this->languageManager->getLanguages();
     $language = ConfigurableLanguage::load($languages[$langcode]->getId());
-    $language->set('weight', 1);
+    // Make $language the last.
+    $language->set('weight', 4);
     $language->save();
     $this->languageManager->reset();