diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index f1e0be1..e78e40f 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1550,12 +1550,12 @@ function install_import_translations(&$install_state) {
 
   $langcode = $install_state['parameters']['langcode'];
   $language = ConfigurableLanguage::createFromLangcode($langcode);
-  $language->set('default', TRUE);
   $language->save();
 
-  // If a non-English language was selected, remove English and import the
-  // translations.
+  // If a non-English language was selected, change the default language,
+  // remove English and import the translations.
   if ($langcode != 'en') {
+    \Drupal::config('system.site')->set('langcode', $langcode)->save();
     entity_delete_multiple('configurable_language', array('en'));
 
     // Set up a batch to import translations for the newly added language.
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index c1069a1..a5bd308 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -1037,7 +1037,7 @@ protected function compileContainer() {
     $default_language_values = Language::$defaultValues;
     if ($system = $this->getConfigStorage()->read('system.site')) {
       if ($default_language_values['id'] != $system['langcode']) {
-        $default_language_values = array('id' => $system['langcode'], 'default' => TRUE);
+        $default_language_values = array('id' => $system['langcode']);
       }
     }
     $container->setParameter('language.default_values', $default_language_values);
diff --git a/core/lib/Drupal/Core/Language/Language.php b/core/lib/Drupal/Core/Language/Language.php
index 8f72cdc..9e04077 100644
--- a/core/lib/Drupal/Core/Language/Language.php
+++ b/core/lib/Drupal/Core/Language/Language.php
@@ -25,7 +25,6 @@ class Language implements LanguageInterface {
     'direction' => self::DIRECTION_LTR,
     'weight' => 0,
     'locked' => FALSE,
-    'default' => TRUE,
   );
 
   // Properties within the Language are set up as the default language.
@@ -61,13 +60,6 @@ class Language implements LanguageInterface {
   public $weight = 0;
 
   /**
-   * Flag indicating if this is the only site default language.
-   *
-   * @var bool
-   */
-  public $default = FALSE;
-
-  /**
    * Locked indicates a language used by the system, not an actual language.
    *
    * Examples of locked languages are, LANGCODE_NOT_SPECIFIED, und, and
@@ -136,7 +128,7 @@ public function getWeight() {
    * {@inheritdoc}
    */
   public function isDefault() {
-    return $this->default;
+    return static::getDefaultLangcode() == $this->getId();
   }
 
   /**
@@ -156,4 +148,15 @@ public static function sort(&$languages) {
     });
   }
 
+  /**
+   * Gets the default langcode.
+   *
+   * @return string
+   *   The current default langcode.
+   */
+  protected static function getDefaultLangcode() {
+    $language = \Drupal::service('language.default')->get();
+    return $language->getId();
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Language/LanguageDefault.php b/core/lib/Drupal/Core/Language/LanguageDefault.php
index 1ca8009..4454489 100644
--- a/core/lib/Drupal/Core/Language/LanguageDefault.php
+++ b/core/lib/Drupal/Core/Language/LanguageDefault.php
@@ -53,7 +53,6 @@ public function get() {
    *   The default language.
    */
   public function set(LanguageInterface $language) {
-    $language->default = TRUE;
     $this->language = $language;
   }
 
diff --git a/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php b/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php
index 1c4a919..62346a1 100644
--- a/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php
+++ b/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php
@@ -119,7 +119,8 @@ function testPerUserLoginFloodControl() {
    * Tests compatibility with locale/UI translation.
    */
   function testLocale() {
-    ConfigurableLanguage::create(array('id' => 'de', 'label' => 'German', 'default' => TRUE))->save();
+    ConfigurableLanguage::createFromLangcode('de')->save();
+    \Drupal::config('system.site')->set('langcode', 'de')->save();
 
     $account = $this->drupalCreateUser();
 
diff --git a/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php b/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php
index 82f4d37..be24fb9 100644
--- a/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php
+++ b/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php
@@ -67,9 +67,7 @@ function testSiteNameTranslation() {
     // overrides still work.
     $language_manager = \Drupal::languageManager()->reset();
     $this->assertTrue($language_manager->isMultilingual(), 'The test site is multilingual.');
-    $language = ConfigurableLanguage::load('xx');
-    $language->set('default', TRUE);
-    $language->save();
+    \Drupal::config('system.site')->set('langcode', 'xx')->save();
 
     ConfigurableLanguage::load('en')->delete();
     $this->assertFalse($language_manager->isMultilingual(), 'The test site is monolingual.');
diff --git a/core/modules/language/language.module b/core/modules/language/language.module
index 96c0a3f..d60d42e 100644
--- a/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -444,10 +444,10 @@ function language_negotiation_url_prefixes_update() {
   foreach (\Drupal::languageManager()->getLanguages() as $language) {
     // The prefix for this language should be updated if it's not assigned yet
     // or the prefix is set to the empty string.
-    if (empty($prefixes[$language->id])) {
+    if (empty($prefixes[$language->getId()])) {
       // For the default language, set the prefix to the empty string,
       // otherwise use the langcode.
-      $prefixes[$language->id] = !empty($language->default) ? '' : $language->id;
+      $prefixes[$language->getId()] = $language->isDefault() ? '' : $language->id;
     }
     // Otherwise we keep the configured prefix.
   }
@@ -592,9 +592,7 @@ function language_form_system_regional_settings_alter(&$form, FormStateInterface
  * @see language_form_system_regional_settings_alter()
  */
 function language_system_regional_settings_form_submit($form, FormStateInterface $form_state) {
-  $default_language = ConfigurableLanguage::load($form_state->getValue('site_default_language'));
-  $default_language->set('default', TRUE);
-  $default_language->save();
+  \Drupal::config('system.site')->set('langcode', $form_state->getValue('site_default_language'))->save();
 }
 
 /**
diff --git a/core/modules/language/language.services.yml b/core/modules/language/language.services.yml
index 1eeb597..eae3af5 100644
--- a/core/modules/language/language.services.yml
+++ b/core/modules/language/language.services.yml
@@ -9,6 +9,7 @@ services:
       - [initLanguageManager]
   language.config_subscriber:
     class: Drupal\language\EventSubscriber\ConfigSubscriber
+    arguments: ['@language_manager', '@language.default']
     tags:
       - { name: event_subscriber }
   language.config_factory_override:
diff --git a/core/modules/language/src/Entity/ConfigurableLanguage.php b/core/modules/language/src/Entity/ConfigurableLanguage.php
index 2f95b9e..bcdf7e2 100644
--- a/core/modules/language/src/Entity/ConfigurableLanguage.php
+++ b/core/modules/language/src/Entity/ConfigurableLanguage.php
@@ -7,12 +7,10 @@
 
 namespace Drupal\language\Entity;
 
-use Drupal\Core\Language\Language as LanguageObject;
 use Drupal\Core\Config\Entity\ConfigEntityBase;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Language\LanguageManager;
 use Drupal\language\ConfigurableLanguageManager;
-use Drupal\Core\Language\Language;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 use Drupal\language\Exception\DeleteDefaultLanguageException;
 use Drupal\language\ConfigurableLanguageInterface;
@@ -83,21 +81,6 @@ class ConfigurableLanguage extends ConfigEntityBase implements ConfigurableLangu
   public $locked = FALSE;
 
   /**
-   * Flag to indicate if the language entity is the default site language.
-   *
-   * This property is not saved to the language entity since there can be only
-   * one default language. It is saved to system.site:langcode and set on the
-   * container using the language.default service in when the entity is saved.
-   * The value is set correctly when a language entity is created or loaded.
-   *
-   * @see \Drupal\language\Entity\ConfigurableLanguage::postSave()
-   * @see \Drupal\language\Entity\ConfigurableLanguage::isDefault()
-   *
-   * @var bool
-   */
-  protected $default;
-
-  /**
    * Used during saving to detect when the site becomes multilingual.
    *
    * This property is not saved to the language entity, but is needed for
@@ -111,16 +94,10 @@ class ConfigurableLanguage extends ConfigEntityBase implements ConfigurableLangu
   protected $preSaveMultilingual;
 
   /**
-   * Checks if the language entity is the site default language.
-   *
-   * @return bool
-   *   TRUE if the language entity is the site default language, FALSE if not.
+   * {@inheritdoc}
    */
   public function isDefault() {
-    if (!isset($this->default)) {
-      return static::getDefaultLangcode() == $this->id();
-    }
-    return $this->default;
+    return static::getDefaultLangcode() == $this->id();
   }
 
   /**
@@ -144,24 +121,14 @@ public function preSave(EntityStorageInterface $storage) {
   public function postSave(EntityStorageInterface $storage, $update = TRUE) {
     parent::postSave($storage, $update);
 
-    // Only set the default language and save it to system.site configuration if
-    // it needs to updated.
-    if ($this->isDefault() && static::getDefaultLangcode() != $this->id()) {
-      // Update the config. Saving the configuration fires and event that causes
-      // the container to be rebuilt.
-      \Drupal::config('system.site')->set('langcode', $this->id())->save();
-      \Drupal::service('language.default')->set($this->toLanguageObject());
-    }
-
     $language_manager = \Drupal::languageManager();
     $language_manager->reset();
     if ($language_manager instanceof ConfigurableLanguageManagerInterface) {
       $language_manager->updateLockedLanguageWeights();
     }
 
-    // Update URL Prefixes for all languages after the new default language is
-    // propagated and the LanguageManagerInterface::getLanguages() cache is
-    // flushed.
+    // Update URL Prefixes for all languages after the
+    // LanguageManagerInterface::getLanguages() cache is flushed.
     language_negotiation_url_prefixes_update();
 
     // If after adding this language the site will become multilingual, we need
@@ -176,26 +143,6 @@ public function postSave(EntityStorageInterface $storage, $update = TRUE) {
   }
 
   /**
-   * Converts the ConfigurableLanguage entity to a Core Language value object.
-   *
-   * @todo fix return type hint after https://drupal.org/node/2246665 and
-   *   https://drupal.org/node/2246679.
-   *
-   * @return \Drupal\Core\Language\LanguageInterface
-   *   The language configuration entity expressed as a Language value object.
-   */
-  protected function toLanguageObject() {
-    return new LanguageObject(array(
-      'id' => $this->id(),
-      'name' => $this->label(),
-      'direction' => $this->direction,
-      'weight' => $this->weight,
-      'locked' => $this->locked,
-      'default' => $this->default,
-    ));
-  }
-
-  /**
    * {@inheritdoc}
    *
    * @throws \DeleteDefaultLanguageException
@@ -229,18 +176,6 @@ public static function postDelete(EntityStorageInterface $storage, array $entiti
   }
 
   /**
-   * {@inheritdoc}
-   */
-  public function get($property_name) {
-    if ($property_name == 'default') {
-      return $this->isDefault();
-    }
-    else {
-      return parent::get($property_name);
-    }
-  }
-
-  /**
    * Gets the default langcode.
    *
    * @return string
diff --git a/core/modules/language/src/EventSubscriber/ConfigSubscriber.php b/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
index 1373a25..2b1c73c 100644
--- a/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
+++ b/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\language\EventSubscriber;
 
+use Drupal\Core\Language\LanguageDefault;
+use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\Core\PhpStorage\PhpStorageFactory;
 use Drupal\Core\Config\ConfigCrudEvent;
 use Drupal\Core\Config\ConfigEvents;
@@ -18,6 +20,33 @@
 class ConfigSubscriber implements EventSubscriberInterface {
 
   /**
+   * The language manager.
+   *
+   * @var \Drupal\Core\Language\LanguageManagerInterface
+   */
+  protected $languageManager;
+
+  /**
+   * The default language.
+   *
+   * @var \Drupal\Core\Language\LanguageDefault
+   */
+  protected $languageDefault;
+
+  /**
+   * Constructs a new class object.
+   *
+   * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
+   *   The language manager.
+   * @param \Drupal\Core\Language\LanguageDefault $language_default
+   *   The default language.
+   */
+  public function __construct(LanguageManagerInterface $language_manager, LanguageDefault $language_default) {
+    $this->languageManager = $language_manager;
+    $this->languageDefault = $language_default;
+  }
+
+  /**
    * Causes the container to be rebuilt on the next request.
    *
    * @param ConfigCrudEvent $event
@@ -26,6 +55,13 @@ class ConfigSubscriber implements EventSubscriberInterface {
   public function onConfigSave(ConfigCrudEvent $event) {
     $saved_config = $event->getConfig();
     if ($saved_config->getName() == 'system.site' && $event->isChanged('langcode')) {
+      $language = $this->languageManager->getLanguage($saved_config->get('langcode'));
+      // During an import the language might not exist yet.
+      if ($language) {
+        $this->languageDefault->set($language);
+        $this->languageManager->reset();
+        language_negotiation_url_prefixes_update();
+      }
       // Trigger a container rebuild on the next request by deleting compiled
       // from PHP storage.
       PhpStorageFactory::get('service_container')->deleteAll();
diff --git a/core/modules/language/src/Form/NegotiationUrlForm.php b/core/modules/language/src/Form/NegotiationUrlForm.php
index e2e241e..f28a53d 100644
--- a/core/modules/language/src/Form/NegotiationUrlForm.php
+++ b/core/modules/language/src/Form/NegotiationUrlForm.php
@@ -76,7 +76,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       $t_args = array('%language' => $language->name, '%langcode' => $language->id);
       $form['prefix'][$langcode] = array(
         '#type' => 'textfield',
-        '#title' => $language->default ? $this->t('%language (%langcode) path prefix (Default language)', $t_args) : $this->t('%language (%langcode) path prefix', $t_args),
+        '#title' => $language->isDefault() ? $this->t('%language (%langcode) path prefix (Default language)', $t_args) : $this->t('%language (%langcode) path prefix', $t_args),
         '#maxlength' => 64,
         '#default_value' => isset($prefixes[$langcode]) ? $prefixes[$langcode] : '',
         '#field_prefix' => $base_url . '/',
@@ -106,7 +106,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       $value = $form_state->getValue(array('prefix', $langcode));
 
       if ($value === '') {
-        if (!$language->default && $form_state->getValue('language_negotiation_url_part') == LanguageNegotiationUrl::CONFIG_PATH_PREFIX) {
+        if (!$language->isDefault() && $form_state->getValue('language_negotiation_url_part') == LanguageNegotiationUrl::CONFIG_PATH_PREFIX) {
           // Throw a form error if the prefix is blank for a non-default language,
           // although it is required for selected negotiation type.
           $form_state->setErrorByName("prefix][$langcode", $this->t('The prefix may only be left blank for the default language.'));
@@ -130,7 +130,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       $value = $form_state->getValue(array('domain', $langcode));
 
       if ($value === '') {
-        if (!$language->default && $form_state->getValue('language_negotiation_url_part') == LanguageNegotiationUrl::CONFIG_DOMAIN) {
+        if (!$language->isDefault() && $form_state->getValue('language_negotiation_url_part') == LanguageNegotiationUrl::CONFIG_DOMAIN) {
           // Throw a form error if the domain is blank for a non-default language,
           // although it is required for selected negotiation type.
           $form_state->setErrorByName("domain][$langcode", $this->t('The domain may only be left blank for the default language.'));
diff --git a/core/modules/language/src/LanguageServiceProvider.php b/core/modules/language/src/LanguageServiceProvider.php
index 0561814..be89900 100644
--- a/core/modules/language/src/LanguageServiceProvider.php
+++ b/core/modules/language/src/LanguageServiceProvider.php
@@ -100,7 +100,7 @@ protected function getDefaultLanguageValues() {
     $system = $config_storage->read('system.site');
     $default_language = $config_storage->read(static::CONFIG_PREFIX . $system['langcode']);
     if (is_array($default_language)) {
-      return $default_language + array('default' => TRUE);
+      return $default_language;
     }
     return FALSE;
   }
diff --git a/core/modules/language/src/Tests/LanguageConfigurationElementTest.php b/core/modules/language/src/Tests/LanguageConfigurationElementTest.php
index 4f3d880..6815955 100644
--- a/core/modules/language/src/Tests/LanguageConfigurationElementTest.php
+++ b/core/modules/language/src/Tests/LanguageConfigurationElementTest.php
@@ -83,18 +83,16 @@ public function testDefaultLangcode() {
     $old_default = \Drupal::languageManager()->getDefaultLanguage();
     // Ensure the language entity default value is correct.
     $configurable_language = entity_load('configurable_language', $old_default->getId());
-    $this->assertTrue($configurable_language->get('default'), 'The en language entity is flagged as the default language.');
+    $this->assertTrue($configurable_language->isDefault(), 'The en language entity is flagged as the default language.');
 
-    $new_default = ConfigurableLanguage::load('cc');
-    $new_default->set('default', TRUE);
-    $new_default->save();
+    \Drupal::config('system.site')->set('langcode', 'cc')->save();
     language_save_default_configuration('custom_type', 'custom_bundle', array('langcode' => 'site_default', 'language_show' => TRUE));
     $langcode = language_get_default_langcode('custom_type', 'custom_bundle');
     $this->assertEqual($langcode, 'cc');
 
     // Ensure the language entity default value is correct.
     $configurable_language = entity_load('configurable_language', $old_default->getId());
-    $this->assertFalse($configurable_language->get('default'), 'The en language entity is not flagged as the default language.');
+    $this->assertFalse($configurable_language->isDefault(), 'The en language entity is not flagged as the default language.');
     $configurable_language = entity_load('configurable_language', 'cc');
     // Check calling the
     // \Drupal\language\Entity\ConfigurableLanguage::isDefault() method
diff --git a/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php b/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php
index 44776bb..70b0d69 100644
--- a/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php
+++ b/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php
@@ -42,13 +42,8 @@ function testDependencyInjectedNewLanguage() {
   function testDependencyInjectedNewDefaultLanguage() {
     $default_language = ConfigurableLanguage::load(\Drupal::languageManager()->getDefaultLanguage()->getId());
     // Change the language default object to different values.
-    ConfigurableLanguage::create(array(
-      'id' => 'fr',
-      'label' => 'French',
-      'direction' => Language::DIRECTION_LTR,
-      'weight' => 0,
-      'default' => TRUE,
-    ))->save();
+    ConfigurableLanguage::createFromLangcode('fr')->save();
+    \Drupal::config('system.site')->set('langcode', 'fr')->save();
 
     // The language system creates a Language object which contains the
     // same properties as the new default language object.
@@ -65,8 +60,8 @@ function testDependencyInjectedNewDefaultLanguage() {
     }
 
     // Re-save the previous default language and the delete should work.
-    $default_language->set('default', TRUE);
-    $default_language->save();
+    \Drupal::config('system.site')->set('langcode', $default_language->getId())->save();
+
     entity_delete_multiple('configurable_language', array('fr'));
     $result = \Drupal::languageManager()->getCurrentLanguage();
     $this->assertIdentical($result->id, $default_language->id);
diff --git a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
index 76720e8..4753539 100644
--- a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
@@ -89,9 +89,8 @@ function testUILanguageNegotiation() {
     // is for some reason not found when doing translate search. This might
     // be some bug.
     $default_language = \Drupal::languageManager()->getDefaultLanguage();
-    $language = ConfigurableLanguage::createFromLangcode($langcode_browser_fallback);
-    $language->set('default', TRUE);
-    $language->save();
+    ConfigurableLanguage::createFromLangcode($langcode_browser_fallback)->save();
+    \Drupal::config('system.site')->set('langcode', $langcode_browser_fallback)->save();
     ConfigurableLanguage::createFromLangcode($langcode)->save();
 
     // We will look for this string in the admin/config screen to see if the
@@ -104,9 +103,7 @@ function testUILanguageNegotiation() {
     // Now the t()'ed string is in db so switch the language back to default.
     // This will rebuild the container so we need to rebuild the container in
     // the test environment.
-    $default_language = ConfigurableLanguage::load($default_language->getId());
-    $default_language->set('default', TRUE);
-    $default_language->save();
+    \Drupal::config('system.site')->set('langcode', $default_language->getId())->save();
     \Drupal::config('language.negotiation')->set('url.prefixes.en', '')->save();
     $this->rebuildContainer();
 
diff --git a/core/modules/locale/src/Tests/LocaleLocaleLookupTest.php b/core/modules/locale/src/Tests/LocaleLocaleLookupTest.php
index 07f6f48..96f5a26 100644
--- a/core/modules/locale/src/Tests/LocaleLocaleLookupTest.php
+++ b/core/modules/locale/src/Tests/LocaleLocaleLookupTest.php
@@ -31,9 +31,9 @@ public function setUp() {
     parent::setUp();
 
     // Change the language default object to different values.
-    $language = ConfigurableLanguage::createFromLangcode('fr');
-    $language->set('default', TRUE);
-    $language->save();
+    ConfigurableLanguage::createFromLangcode('fr')->save();
+    \Drupal::config('system.site')->set('langcode', 'fr')->save();
+
     $this->drupalLogin($this->root_user);
   }
 
diff --git a/core/modules/menu_ui/src/Tests/MenuLanguageTest.php b/core/modules/menu_ui/src/Tests/MenuLanguageTest.php
index f5d32f8..f74fb09 100644
--- a/core/modules/menu_ui/src/Tests/MenuLanguageTest.php
+++ b/core/modules/menu_ui/src/Tests/MenuLanguageTest.php
@@ -150,9 +150,7 @@ function testMenuLanguageRemovedEnglish() {
 
     // Remove English language. To do that another language has to be set as
     // default.
-    $language = ConfigurableLanguage::load('cs');
-    $language->set('default', TRUE);
-    $language->save();
+    \Drupal::config('system.site')->set('langcode', 'cs')->save();
     entity_delete_multiple('configurable_language', array('en'));
 
     // Save the menu again and check if the language is still the same.
diff --git a/core/modules/system/src/Tests/Common/FormatDateTest.php b/core/modules/system/src/Tests/Common/FormatDateTest.php
index 9c75f29..f8ad3b7 100644
--- a/core/modules/system/src/Tests/Common/FormatDateTest.php
+++ b/core/modules/system/src/Tests/Common/FormatDateTest.php
@@ -96,9 +96,7 @@ function testFormatDate() {
     $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'Europe/London', 'en'), 'Monday, 26-Mar-07 01:00:00 BST', 'Test a different time zone.');
 
     // Change the default language and timezone.
-    $language = ConfigurableLanguage::load(static::LANGCODE);
-    $language->set('default', TRUE);
-    $language->save();
+    \Drupal::config('system.site')->set('langcode', static::LANGCODE)->save();
     date_default_timezone_set('America/Los_Angeles');
 
     $this->assertIdentical(format_date($timestamp, 'custom', 'l, d-M-y H:i:s T', 'America/Los_Angeles', 'en'), 'Sunday, 25-Mar-07 17:00:00 PDT', 'Test a different language.');
diff --git a/core/modules/system/src/Tests/Theme/TwigTransTest.php b/core/modules/system/src/Tests/Theme/TwigTransTest.php
index 98a6e9f..7825259 100644
--- a/core/modules/system/src/Tests/Theme/TwigTransTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigTransTest.php
@@ -70,9 +70,7 @@ protected function setUp() {
     $this->installLanguages();
 
     // Assign Lolspeak (xx) to be the default language.
-    $language = ConfigurableLanguage::load('xx');
-    $language->set('default', TRUE);
-    $language->save();
+    \Drupal::config('system.site')->set('langcode', 'xx')->save();
     $this->rebuildContainer();
 
     // Check that lolspeak is the default language for the site.
diff --git a/core/modules/taxonomy/src/Tests/TermLanguageTest.php b/core/modules/taxonomy/src/Tests/TermLanguageTest.php
index be67e5d..cb64143 100644
--- a/core/modules/taxonomy/src/Tests/TermLanguageTest.php
+++ b/core/modules/taxonomy/src/Tests/TermLanguageTest.php
@@ -95,9 +95,7 @@ function testDefaultTermLanguage() {
 
     // Change the default language of the site and check if the default terms
     // language is still correctly selected.
-    $new_default = ConfigurableLanguage::load('cc');
-    $new_default->set('default', TRUE);
-    $new_default->save();
+    \Drupal::config('system.site')->set('langcode', 'cc')->save();
     $edit = array(
       'default_language[langcode]' => 'site_default',
       'default_language[language_show]' => TRUE,
diff --git a/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php b/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php
index 97ed8a7..281539b 100644
--- a/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php
+++ b/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php
@@ -56,9 +56,8 @@ public function testCreateView() {
     $random_description = $this->randomMachineName();
 
     // Add a new language and mark it as default.
-    $language = ConfigurableLanguage::createFromLangcode('it');
-    $language->set('default', TRUE);
-    $language->save();
+    ConfigurableLanguage::createFromLangcode('it')->save();
+    \Drupal::config('system.site')->set('langcode', 'it')->save();
 
     $form_state->setValues([
       'id' => $random_id,
diff --git a/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php b/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php
index 75e1fd8..e15cbac 100644
--- a/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php
@@ -49,9 +49,26 @@ public function testGetDirection() {
    * @covers ::isDefault()
    */
   public function testIsDefault() {
-    $language_code = $this->randomMachineName(2);
-    $language = new Language(array('id' => $language_code, 'default' => TRUE));
+    $language_default = $this->getMockBuilder('Drupal\Core\Language\LanguageDefault')->disableOriginalConstructor()->getMock();
+    $container = $this->getMock('Symfony\Component\DependencyInjection\ContainerInterface');
+    $container->expects($this->any())
+      ->method('get')
+      ->with('language.default')
+      ->will($this->returnValue($language_default));
+    \Drupal::setContainer($container);
+
+    $language = new Language(array('id' => $this->randomMachineName(2)));
+    // Set up the LanguageDefault to return different default languages on
+    // consecutive calls.
+    $language_default->expects($this->any())
+      ->method('get')
+      ->willReturnOnConsecutiveCalls(
+        $language,
+        new Language(array('id' => $this->randomMachineName(2)))
+      );
+
     $this->assertTrue($language->isDefault());
+    $this->assertFalse($language->isDefault());
   }
 
   /**