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
@@ -430,6 +430,7 @@
   $language_entity->label = isset($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();
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
@@ -9,6 +9,8 @@
 
 use Drupal\Core\Config\Entity\ConfigEntityBase;
 use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\language\ConfigurableLanguageManager;
+use Drupal\language\ConfigurableLanguageManagerInterface;
 use Drupal\language\Exception\DeleteDefaultLanguageException;
 use Drupal\language\LanguageInterface;