diff --git a/core/modules/ckeditor/src/Tests/CKEditorTest.php b/core/modules/ckeditor/src/Tests/CKEditorTest.php
index fedffe8..e066a6e 100644
--- a/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\ckeditor\Tests;
 
+use Drupal\Core\Language\LanguageDefault;
 use Drupal\simpletest\KernelTestBase;
 use Drupal\language\Entity\ConfigurableLanguage;
 
@@ -380,6 +381,7 @@ function testJSTranslation() {
     $this->enableModules(array('language', 'locale'));
     $this->installSchema('locale', 'locales_source');
     $this->installSchema('locale', 'locales_location');
+    $this->installSchema('locale', 'locales_target');
     $editor = entity_load('editor', 'filtered_html');
     $this->ckeditor->getJSSettings($editor);
     $localeStorage = $this->container->get('locale.storage');
@@ -398,8 +400,16 @@ function testJSTranslation() {
    *   language set in this assertion.
    */
   protected function assertCKEditorLanguage($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 = entity_load('editor', 'filtered_html');
     $settings = $this->ckeditor->getJSSettings($editor);
     $this->assertEqual($settings['language'], $langcode);