diff -u b/core/modules/language/language.module b/core/modules/language/language.module
--- b/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -430,7 +430,6 @@
   $language_entity->label = isset($language->name) ? $language->name : '';
   $language_entity->direction = isset($language->direction) ? $language->direction : '0';
   $language_entity->locked = !empty($language->locked);
-  $language_entity->default = !empty($language->default);
   $language_entity->weight = isset($language->weight) ? $language->weight : 0;
 
   $language_entity->save();
@@ -442,6 +441,13 @@
     watchdog('language', 'The %language (%langcode) language has been updated.', $t_args);
   }
 
+  if (!empty($language->default)) {
+    // Update the config. Saving the configuration fires and event that causes
+    // the container to be rebuilt.
+    \Drupal::config('system.site')->set('langcode', $language->id)->save();
+    \Drupal::service('language.default')->set($language);
+  }
+
   return $language;
 }
 
@@ -682,4 +688,13 @@
   $language = $languages[$form_state['values']['site_default_language']];
-  $language->default = TRUE;
-  language_save($language);
+
+  \Drupal::config('system.site')->set('langcode', $language->id)->save();
+  \Drupal::service('language.default')->set($language);
+
+  \Drupal::languageManager()->reset();
+
+  // Update URL Prefixes for all languages after the new default language is
+  // propagated and the LanguageManagerInterface::getLanguages() cache is
+  // flushed.
+  language_negotiation_url_prefixes_update();
+
 }
diff -u b/core/modules/language/lib/Drupal/language/Entity/Language.php b/core/modules/language/lib/Drupal/language/Entity/Language.php
--- b/core/modules/language/lib/Drupal/language/Entity/Language.php
+++ b/core/modules/language/lib/Drupal/language/Entity/Language.php
@@ -99,13 +99,6 @@
     // Save the record and inform others about the change.
     $multilingual = \Drupal::languageManager()->isMultilingual();
 
-    if (!empty($this->default)) {
-      // Update the config. Saving the configuration fires and event that causes
-      // the container to be rebuilt.
-      \Drupal::config('system.site')->set('langcode', $this->id())->save();
-      \Drupal::service('language.default')->set(\Drupal::languageManager()->getLanguage($this->id()));
-    }
-
     $language_manager = \Drupal::languageManager();
     $language_manager->reset();
     if ($language_manager instanceof ConfigurableLanguageManagerInterface) {