diff --git a/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php b/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
index c8cb932..beba1f5 100644
--- a/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
+++ b/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
@@ -258,11 +258,14 @@ public function getJSSettings(EditorEntity $editor) {
     // Fall back on English if no matching language code was found.
     $display_langcode = 'en';
 
-    // Map the interface language code to a CKEditor translation.
-    $ckeditor_langcodes = $this->getLangcodes();
-    $language_interface = $this->languageManager->getCurrentLanguage();
-    if (isset($ckeditor_langcodes[$language_interface->getId()])) {
-      $display_langcode = $ckeditor_langcodes[$language_interface->getId()];
+    // Map the interface language code to a CKEditor translation if interface
+    // translation is enabled.
+    if ($this->moduleHandler->moduleExists('locale')) {
+      $ckeditor_langcodes = $this->getLangcodes();
+      $language_interface = $this->languageManager->getCurrentLanguage();
+      if (isset($ckeditor_langcodes[$language_interface->getId()])) {
+        $display_langcode = $ckeditor_langcodes[$language_interface->getId()];
+      }
     }
 
     // Next, set the most fundamental CKEditor settings.
diff --git a/core/modules/ckeditor/src/Tests/CKEditorTest.php b/core/modules/ckeditor/src/Tests/CKEditorTest.php
index 9133ee0..f681671 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -8,8 +8,8 @@
 namespace Drupal\ckeditor\Tests;
 
 use Drupal\simpletest\KernelTestBase;
-use Drupal\editor\Plugin\EditorManager;
-use Drupal\ckeditor\Plugin\Editor\CKEditor;
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\editor\Entity\Editor;
 
 /**
  * Tests for the 'CKEditor' text editor plugin.
@@ -368,6 +368,10 @@ function testLanguages() {
     // Language codes only in CKEditor.
     $this->assertTrue($langcodes['en-au'] == 'en-au', '"en-au" properly resolved');
     $this->assertTrue($langcodes['sr-latn'] == 'sr-latn', '"sr-latn" properly resolved');
+
+    // No locale module, so even though languages are enabled, CKEditor should
+    // still be in English.
+    $this->assertCKEditorLanguage('en');
   }
 
   /**
@@ -377,11 +381,38 @@ function testJSTranslation() {
     $this->enableModules(array('language', 'locale'));
     $this->installSchema('locale', 'locales_source');
     $this->installSchema('locale', 'locales_location');
-    $editor = entity_load('editor', 'filtered_html');
+    $this->installSchema('locale', 'locales_target');
+    $editor = Editor::load('filtered_html');
     $this->ckeditor->getJSSettings($editor);
     $localeStorage = $this->container->get('locale.storage');
     $string = $localeStorage->findString(array('source' => 'Edit Link', 'context' => ''));
     $this->assertTrue(!empty($string), 'String from JavaScript file saved.');
+
+    // With locale module, CKEditor should not adhere to the language selected.
+    $this->assertCKEditorLanguage();
+  }
+
+  /**
+   * Assert that CKEditor picks the expected language when French is default.
+   *
+   * @param string $langcode
+   *   Language code to assert for. Defaults to French. That is the default
+   *   language set in this assertion.
+   */
+  protected function assertCKEditorLanguage($langcode = 'fr') {
+    // Set French as the site default language.
+    ConfigurableLanguage::createFromLangcode('fr')->save();
+    \Drupal::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.
+    $this->container->get('language_manager')->reset();
+    $this->ckeditor = $this->container->get('plugin.manager.editor')->createInstance('ckeditor');
+
+    // Test that we now get the expected language.
+    $editor = Editor::load('filtered_html');
+    $settings = $this->ckeditor->getJSSettings($editor);
+    $this->assertEqual($settings['language'], $langcode);
   }
 
   protected function getDefaultInternalConfig() {