diff --git a/core/lib/Drupal/Core/Language/LanguageManager.php b/core/lib/Drupal/Core/Language/LanguageManager.php
index 22c5289..c38fc10 100644
--- a/core/lib/Drupal/Core/Language/LanguageManager.php
+++ b/core/lib/Drupal/Core/Language/LanguageManager.php
@@ -188,6 +188,8 @@ public function getLanguageName($langcode) {
    */
   public function getDefaultLockedLanguages($weight = 0) {
     $languages = array();
+    // By default set a high weight.
+    $weight = max($weight, 97);
 
     $locked_language = array(
       'default' => FALSE,
diff --git a/core/modules/ckeditor/src/Tests/CKEditorTest.php b/core/modules/ckeditor/src/Tests/CKEditorTest.php
index caf0345..b0bdce8 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -382,7 +382,8 @@ function testLanguages() {
    * Tests that CKEditor plugins participate in JS translation.
    */
   function testJSTranslation() {
-    $this->enableModules(array('language', 'locale'));
+    $this->enableModules(array('locale'));
+    $this->installConfig(['language']);
     $this->installSchema('locale', 'locales_source');
     $this->installSchema('locale', 'locales_location');
     $this->installSchema('locale', 'locales_target');
diff --git a/core/modules/language/config/install/language.entity.und.yml b/core/modules/language/config/install/language.entity.und.yml
index 67caf48..9db876b 100644
--- a/core/modules/language/config/install/language.entity.und.yml
+++ b/core/modules/language/config/install/language.entity.und.yml
@@ -1,7 +1,7 @@
 id: und
 label: 'Not specified'
 direction: 'ltr'
-weight: 1
+weight: 98
 locked: true
 status: true
 langcode: en
diff --git a/core/modules/language/config/install/language.entity.zxx.yml b/core/modules/language/config/install/language.entity.zxx.yml
index 7f02cf7..9c88e04 100644
--- a/core/modules/language/config/install/language.entity.zxx.yml
+++ b/core/modules/language/config/install/language.entity.zxx.yml
@@ -1,7 +1,7 @@
 id: zxx
 label: 'Not applicable'
 direction: 'ltr'
-weight: 2
+weight: 99
 locked: true
 status: true
 langcode: en
diff --git a/core/modules/language/src/Entity/ConfigurableLanguage.php b/core/modules/language/src/Entity/ConfigurableLanguage.php
index a754654..44b96fd 100644
--- a/core/modules/language/src/Entity/ConfigurableLanguage.php
+++ b/core/modules/language/src/Entity/ConfigurableLanguage.php
@@ -72,7 +72,7 @@ class ConfigurableLanguage extends ConfigEntityBase implements ConfigurableLangu
    *
    * @var integer
    */
-  protected $weight = 0;
+  protected $weight = NULL;
 
   /**
    * Locked languages cannot be edited.
@@ -121,6 +121,16 @@ public function preSave(EntityStorageInterface $storage) {
     // For the uncommon case of custom languages the label should be given in
     // English.
     $this->langcode = 'en';
+
+    // When adding a new language the weight shouldn't be zero to avoid a
+    // reordering of the languages list when their names change i.e. interface
+    // translation.
+    if (is_null($this->getWeight())) {
+      // 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 +141,7 @@ 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 +183,8 @@ 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/LanguageConfigurationTest.php b/core/modules/language/src/Tests/LanguageConfigurationTest.php
index a5efb2f..d94fcf4 100644
--- a/core/modules/language/src/Tests/LanguageConfigurationTest.php
+++ b/core/modules/language/src/Tests/LanguageConfigurationTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\language\Tests;
 
 use Drupal\Core\Language\LanguageInterface;
+use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -28,6 +29,9 @@ class LanguageConfigurationTest extends WebTestBase {
    * Functional tests for adding, editing and deleting languages.
    */
   function testLanguageConfiguration() {
+    // Ensure the after installing the language module the weight of the english
+    // language is still 0.
+    $this->assertEqual(ConfigurableLanguage::load('en')->getWeight(), 0, 'The english language has a weight of 0.');
 
     // User to add and remove language.
     $admin_user = $this->drupalCreateUser(array('administer languages', 'access administration pages'));
@@ -103,6 +107,24 @@ function testLanguageConfiguration() {
     $this->drupalPostForm('admin/config/regional/language/delete/en', array(), t('Delete'));
     $this->rebuildContainer();
     $this->assertRaw(t('The %language (%langcode) language has been removed.', array('%language' => 'English', '%langcode' => 'en')));
+
+    // Ensure that french language has a weight of 1 after being created through the UI.
+    $french = ConfigurableLanguage::load('fr');
+    $this->assertEqual($french->getWeight(), 1, 'The French language has a weight of 1.');
+    // Ensure that french language can now have a weight of 0.
+    $french->setWeight(0)->save();
+    $this->assertEqual($french->getWeight(), 0, 'The French language has a weight of 0.');
+    // Ensure that new languages get the last weight by default.
+    $afrikaans = ConfigurableLanguage::createFromLangcode('af');
+    $afrikaans->save();
+    $this->assertEqual($afrikaans->getWeight(), 1, 'The Afrikaans language has a weight of 1.');
+    $afrikaans->setWeight(0)->save();
+    $this->assertEqual($afrikaans->getWeight(), 0, 'The Afrikaans language has a weight of 0.');
+    // Ensure that a new language can be created with a weight of 0.
+    $arabic = ConfigurableLanguage::createFromLangcode('ar');
+    $arabic->setWeight(0)->save();
+    $this->assertEqual($arabic->getWeight(), 0, 'The Arabic language has a weight of 0.');
+
     $edit = array(
       'predefined_langcode' => 'de',
     );
diff --git a/core/modules/language/src/Tests/LanguageListTest.php b/core/modules/language/src/Tests/LanguageListTest.php
index 8ec846c..608485e 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 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 = $this->randomMachineName(16);
diff --git a/core/modules/system/src/Tests/Entity/EntityTranslationTest.php b/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
index 2e8a3b3..98362a7 100644
--- a/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
+++ b/core/modules/system/src/Tests/Entity/EntityTranslationTest.php
@@ -504,7 +504,8 @@ protected function doTestLanguageFallback($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();