diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index a6e918f0bed9d7a47de29f8397c38e3fe27d5530..52cca498ec225c2ddbdcd3720d7afabe55a5d8ef 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1664,10 +1664,7 @@ function install_download_additional_translations_operations(&$install_state) {
   // If a non-English language was selected, change the default language and
   // remove English.
   if ($langcode != 'en') {
-    \Drupal::configFactory()->getEditable('system.site')
-      ->set('langcode', $langcode)
-      ->set('default_langcode', $langcode)
-      ->save();
+    \Drupal::configFactory()->getEditable('system.site')->set('langcode', $langcode)->save();
     \Drupal::service('language.default')->set($language);
     if (empty($install_state['profile_info']['keep_english'])) {
       entity_delete_multiple('configurable_language', array('en'));
diff --git a/core/includes/install.inc b/core/includes/install.inc
index 61d286bdec821373b79e9343463fb0c7b00114b5..e247378750d159ae0db9516750614578760c33c7 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -620,7 +620,6 @@ function drupal_install_system($install_state) {
   if (isset($install_state['parameters']['langcode'])) {
     \Drupal::configFactory()->getEditable('system.site')
       ->set('langcode', $install_state['parameters']['langcode'])
-      ->set('default_langcode', $install_state['parameters']['langcode'])
       ->save();
   }
 }
diff --git a/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php b/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php
index 5790294609347bd6ce521b12303f1a265ba7cf9f..44c14f198645311354a754dd68def41b6cf0465b 100644
--- a/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php
+++ b/core/modules/basic_auth/src/Tests/Authentication/BasicAuthTest.php
@@ -145,7 +145,7 @@ function testPerUserLoginFloodControl() {
    */
   function testLocale() {
     ConfigurableLanguage::createFromLangcode('de')->save();
-    $this->config('system.site')->set('default_langcode', 'de')->save();
+    $this->config('system.site')->set('langcode', 'de')->save();
 
     $account = $this->drupalCreateUser();
     $url = Url::fromRoute('router_test.11');
diff --git a/core/modules/ckeditor/src/Tests/CKEditorTest.php b/core/modules/ckeditor/src/Tests/CKEditorTest.php
index 279b56f3b5fce58851aaed1e3216cfe70b44492e..ab303b60d4e69651ef55ae550e3ba4692d82374f 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -406,7 +406,7 @@ function testJSTranslation() {
   protected function assertCKEditorLanguage($langcode = 'fr') {
     // Set French as the site default language.
     ConfigurableLanguage::createFromLangcode('fr')->save();
-    $this->config('system.site')->set('default_langcode', 'fr')->save();
+    $this->config('system.site')->set('langcode', 'fr')->save();
 
     // Reset the language manager so new negotiations attempts will fall back on
     // French. Reinject the language manager CKEditor to use the current one.
diff --git a/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php b/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php
index f21c30c61784ad4a943e3fe9ddb7f9208f2e2d9e..9ecf5ae4a9d09e092f8692c5710871cce8178f27 100644
--- a/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php
+++ b/core/modules/config/src/Tests/ConfigLanguageOverrideWebTest.php
@@ -75,7 +75,7 @@ function testSiteNameTranslation() {
     // overrides still work.
     $language_manager = \Drupal::languageManager()->reset();
     $this->assertTrue($language_manager->isMultilingual(), 'The test site is multilingual.');
-    $this->config('system.site')->set('default_langcode', 'xx')->save();
+    $this->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/src/EventSubscriber/ConfigSubscriber.php b/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
index ef3f65d5ef1307bd877fb610548c5a6ded01b162..2b1c73c6cb5c921a2c69ad28333522e38a79b534 100644
--- a/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
+++ b/core/modules/language/src/EventSubscriber/ConfigSubscriber.php
@@ -54,8 +54,8 @@ public function __construct(LanguageManagerInterface $language_manager, Language
    */
   public function onConfigSave(ConfigCrudEvent $event) {
     $saved_config = $event->getConfig();
-    if ($saved_config->getName() == 'system.site' && $event->isChanged('default_langcode')) {
-      $language = $this->languageManager->getLanguage($saved_config->get('default_langcode'));
+    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);
diff --git a/core/modules/language/src/LanguageListBuilder.php b/core/modules/language/src/LanguageListBuilder.php
index aa018dc47ac45e039b6fd7a23ffdde6ae226e267..b8f64544040a6fa471a03768cad78794a694c1e7 100644
--- a/core/modules/language/src/LanguageListBuilder.php
+++ b/core/modules/language/src/LanguageListBuilder.php
@@ -152,7 +152,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
     // Save the default language if changed.
     $new_id = $form_state->getValue('site_default_language');
     if ($new_id != $this->languageManager->getDefaultLanguage()->getId()) {
-      $this->configFactory->getEditable('system.site')->set('default_langcode', $new_id)->save();
+      $this->configFactory->getEditable('system.site')->set('langcode', $new_id)->save();
       $this->languageManager->reset();
     }
 
diff --git a/core/modules/language/src/LanguageServiceProvider.php b/core/modules/language/src/LanguageServiceProvider.php
index de2fa6ff9ee923f99ed7d8ce30d0901fb6041851..d7c4dddb3fa4895646cd1c1bd5a99a7a8a094cc6 100644
--- a/core/modules/language/src/LanguageServiceProvider.php
+++ b/core/modules/language/src/LanguageServiceProvider.php
@@ -97,7 +97,7 @@ protected function isMultilingual() {
   protected function getDefaultLanguageValues() {
     $config_storage = BootstrapConfigStorageFactory::get();
     $system = $config_storage->read('system.site');
-    $default_language = $config_storage->read(static::CONFIG_PREFIX . $system['default_langcode']);
+    $default_language = $config_storage->read(static::CONFIG_PREFIX . $system['langcode']);
     if (is_array($default_language)) {
       return $default_language;
     }
diff --git a/core/modules/language/src/Tests/LanguageConfigurationElementTest.php b/core/modules/language/src/Tests/LanguageConfigurationElementTest.php
index 1d4ee2753b8f897a3761c1afe95ec7865051d0ef..f4e1378b7299c729a76d9eccb3a20aeb5a1cd871 100644
--- a/core/modules/language/src/Tests/LanguageConfigurationElementTest.php
+++ b/core/modules/language/src/Tests/LanguageConfigurationElementTest.php
@@ -116,7 +116,7 @@ public function testDefaultLangcode() {
     $configurable_language = entity_load('configurable_language', $old_default->getId());
     $this->assertTrue($configurable_language->isDefault(), 'The en language entity is flagged as the default language.');
 
-    $this->config('system.site')->set('default_langcode', 'cc')->save();
+    $this->config('system.site')->set('langcode', 'cc')->save();
     ContentLanguageSettings::loadByEntityTypeBundle('entity_test','custom_bundle')
       ->setLanguageAlterable(TRUE)
       ->setDefaultLangcode(LanguageInterface::LANGCODE_SITE_DEFAULT)
diff --git a/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php b/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php
index 46b30416fc674e66ee4a3f19c2b891a7eb16b77f..1a7a815ec976c0c054f9b0642f1a8dadae6fa20e 100644
--- a/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php
+++ b/core/modules/language/src/Tests/LanguageDependencyInjectionTest.php
@@ -43,7 +43,7 @@ function testDependencyInjectedNewDefaultLanguage() {
     $default_language = ConfigurableLanguage::load(\Drupal::languageManager()->getDefaultLanguage()->getId());
     // Change the language default object to different values.
     ConfigurableLanguage::createFromLangcode('fr')->save();
-    $this->config('system.site')->set('default_langcode', 'fr')->save();
+    $this->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.
@@ -60,7 +60,7 @@ function testDependencyInjectedNewDefaultLanguage() {
     }
 
     // Re-save the previous default language and the delete should work.
-    $this->config('system.site')->set('default_langcode', $default_language->getId())->save();
+    $this->config('system.site')->set('langcode', $default_language->getId())->save();
 
     entity_delete_multiple('configurable_language', array('fr'));
     $result = \Drupal::languageManager()->getCurrentLanguage();
diff --git a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
index 99d4778be6e7af19bb7f4ee28e3c8b40eef6fe87..f801b6ae8889a4b5d9749a63e0d9a02789ed82fb 100644
--- a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
@@ -93,7 +93,7 @@ function testUILanguageNegotiation() {
     // be some bug.
     $default_language = \Drupal::languageManager()->getDefaultLanguage();
     ConfigurableLanguage::createFromLangcode($langcode_browser_fallback)->save();
-    $this->config('system.site')->set('default_langcode', $langcode_browser_fallback)->save();
+    $this->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
@@ -106,7 +106,7 @@ 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.
-    $this->config('system.site')->set('default_langcode', $default_language->getId())->save();
+    $this->config('system.site')->set('langcode', $default_language->getId())->save();
     $this->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 ef53b8c897af6e24794910d9f8743eec6101080b..05220105ffe6043f44c20f5d8789fd70ae0e9402 100644
--- a/core/modules/locale/src/Tests/LocaleLocaleLookupTest.php
+++ b/core/modules/locale/src/Tests/LocaleLocaleLookupTest.php
@@ -32,7 +32,7 @@ public function setUp() {
 
     // Change the language default object to different values.
     ConfigurableLanguage::createFromLangcode('fr')->save();
-    $this->config('system.site')->set('default_langcode', 'fr')->save();
+    $this->config('system.site')->set('langcode', 'fr')->save();
 
     $this->drupalLogin($this->rootUser);
   }
diff --git a/core/modules/locale/src/Tests/LocaleTranslatedSchemaDefinitionTest.php b/core/modules/locale/src/Tests/LocaleTranslatedSchemaDefinitionTest.php
index a5786b135923587835df01680da803be0feba916..f94db02971030bebb53ec4f020470e6b1d6e8f95 100644
--- a/core/modules/locale/src/Tests/LocaleTranslatedSchemaDefinitionTest.php
+++ b/core/modules/locale/src/Tests/LocaleTranslatedSchemaDefinitionTest.php
@@ -30,7 +30,7 @@ class LocaleTranslatedSchemaDefinitionTest extends WebTestBase {
   protected function setUp() {
     parent::setUp();
     ConfigurableLanguage::createFromLangcode('fr')->save();
-    $this->config('system.site')->set('default_langcode', 'fr')->save();
+    $this->config('system.site')->set('langcode', 'fr')->save();
     // Make sure new entity type definitions are processed.
     \Drupal::service('entity.definition_update_manager')->applyUpdates();
     // Clear all caches so that the base field definition, its cache in the
diff --git a/core/modules/menu_ui/src/Tests/MenuLanguageTest.php b/core/modules/menu_ui/src/Tests/MenuLanguageTest.php
index 085722fdf2fdbc072ae50dadbaba898a0afb1ccb..59b045871aa390b0e9453eeb944f922498ff0ed1 100644
--- a/core/modules/menu_ui/src/Tests/MenuLanguageTest.php
+++ b/core/modules/menu_ui/src/Tests/MenuLanguageTest.php
@@ -155,7 +155,7 @@ function testMenuLanguageRemovedEnglish() {
 
     // Remove English language. To do that another language has to be set as
     // default.
-    $this->config('system.site')->set('default_langcode', 'cs')->save();
+    $this->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/config/install/system.site.yml b/core/modules/system/config/install/system.site.yml
index 403e4640967643335e88aa7dc9620d7c975042f7..10e2be2e7e59ea603fe32618799b2fdbe9ff04e7 100644
--- a/core/modules/system/config/install/system.site.yml
+++ b/core/modules/system/config/install/system.site.yml
@@ -9,4 +9,3 @@ page:
 admin_compact_mode: false
 weight_select_max: 100
 langcode: en
-default_langcode: en
diff --git a/core/modules/system/config/schema/system.schema.yml b/core/modules/system/config/schema/system.schema.yml
index ba8fa1598b34dcee0aaa86133d1552806d57df8f..6888a56e253d6db379badaff7a0599b01457614c 100644
--- a/core/modules/system/config/schema/system.schema.yml
+++ b/core/modules/system/config/schema/system.schema.yml
@@ -37,10 +37,7 @@ system.site:
       label: 'Weight element maximum value'
     langcode:
       type: string
-      label: 'Language code'
-    default_langcode:
-      type: string
-      label: 'Site default language code'
+      label: 'Default language'
     mail_notification:
       type: string
       label: 'Notification email address'
diff --git a/core/modules/system/src/Tests/Common/FormatDateTest.php b/core/modules/system/src/Tests/Common/FormatDateTest.php
index 9d9a265f225206a5f0e3ce9b33c76a3466662202..63576fece142306d689fdb7ff26caf317e267f16 100644
--- a/core/modules/system/src/Tests/Common/FormatDateTest.php
+++ b/core/modules/system/src/Tests/Common/FormatDateTest.php
@@ -96,7 +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.
-    $this->config('system.site')->set('default_langcode', static::LANGCODE)->save();
+    $this->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 85ba19a22fcf6f5fbddd68d0377f97a05963e8cf..7f21b2dee41475bc6ad1d8fbe434f1a17292eacb 100644
--- a/core/modules/system/src/Tests/Theme/TwigTransTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigTransTest.php
@@ -70,7 +70,7 @@ protected function setUp() {
     $this->installLanguages();
 
     // Assign Lolspeak (xx) to be the default language.
-    $this->config('system.site')->set('default_langcode', 'xx')->save();
+    $this->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 c679204b11f7e321874da4b413545842eb10e2d6..011404d102f420491762b0bc8ed2816f6d1fc73f 100644
--- a/core/modules/taxonomy/src/Tests/TermLanguageTest.php
+++ b/core/modules/taxonomy/src/Tests/TermLanguageTest.php
@@ -102,7 +102,7 @@ function testDefaultTermLanguage() {
 
     // Change the default language of the site and check if the default terms
     // language is still correctly selected.
-    $this->config('system.site')->set('default_langcode', 'cc')->save();
+    $this->config('system.site')->set('langcode', 'cc')->save();
     $edit = array(
       'default_language[langcode]' => LanguageInterface::LANGCODE_SITE_DEFAULT,
       'default_language[language_alterable]' => TRUE,
diff --git a/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php b/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php
index fbd6682deac922846c12e089b41dd0dc0340b83f..10cc379c22b7549959bf5ec5babf3e4e5a882bf5 100644
--- a/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php
+++ b/core/modules/views/src/Tests/Wizard/WizardPluginBaseUnitTest.php
@@ -57,7 +57,7 @@ public function testCreateView() {
 
     // Add a new language and mark it as default.
     ConfigurableLanguage::createFromLangcode('it')->save();
-    $this->config('system.site')->set('default_langcode', 'it')->save();
+    $this->config('system.site')->set('langcode', 'it')->save();
 
     $form_state->setValues([
       'id' => $random_id,