reverted:
--- b/core/lib/Drupal/Core/Language/Language.php
+++ a/core/lib/Drupal/Core/Language/Language.php
@@ -79,7 +79,7 @@
    *   An array of property values, keyed by property name, used to construct
    *   the language.
    */
+  public function __construct(array $values = array()) {
-  public function __construct(array $values = []) {
     // Set all the provided properties for the language.
     foreach ($values as $key => $value) {
       if (property_exists($this, $key)) {
diff -u b/core/lib/Drupal/Core/Language/LanguageManager.php b/core/lib/Drupal/Core/Language/LanguageManager.php
--- b/core/lib/Drupal/Core/Language/LanguageManager.php
+++ b/core/lib/Drupal/Core/Language/LanguageManager.php
@@ -340,8 +340,7 @@
    *
    * @return array
    *   An array with language codes as keys, and English and native language
-   *   names as values. Language name information is an array of English and
-   *   native names.
+   *   names as values.
    */
   public static function getUnitedNationsLanguageList() {
     return [
diff -u b/core/modules/ckeditor/ckeditor.libraries.yml b/core/modules/ckeditor/ckeditor.libraries.yml
--- b/core/modules/ckeditor/ckeditor.libraries.yml
+++ b/core/modules/ckeditor/ckeditor.libraries.yml
@@ -79,6 +79,7 @@
     - core/jquery
     - core/drupal
     - core/drupal.vertical-tabs
+    - core/drupalSettings
     # Ensure to run after ckeditor/drupal.ckeditor.admin.
     - ckeditor/drupal.ckeditor.admin
 
@@ -92,3 +93 @@
-    - core/jquery.once
     - core/drupal.vertical-tabs
-    - core/drupalSettings
diff -u b/core/modules/ckeditor/css/plugins/language/ckeditor.language.css b/core/modules/ckeditor/css/plugins/language/ckeditor.language.css
--- b/core/modules/ckeditor/css/plugins/language/ckeditor.language.css
+++ b/core/modules/ckeditor/css/plugins/language/ckeditor.language.css
@@ -8,21 +8,12 @@
- * border. We also append the value of the tag between brackets, eg: '(en)'.
+ * border. We also append the value of the tag between brackets, for example:
+ * '(en)'. Since the html element has a 'lang' attribute too we only target
+ * elements within the html scope.
  */
-[lang] {
+html [lang] {
   outline: 1px dotted gray;
 }
-[lang]:after {
+html [lang]:after {
   content: " ("attr(lang)")";
   font-size: 10px;
   color: #666;
 }
-
-/**
- * The HTML element has a default 'lang' attribute.
- * We don't want styling there.
- */
-html[lang] {
-  outline: none;
-}
-html[lang]:after {
-  content: none;
-}
reverted:
--- b/core/modules/ckeditor/src/Tests/CKEditorTest.php
+++ a/core/modules/ckeditor/src/Tests/CKEditorTest.php
@@ -480,7 +480,6 @@
     return array(
       file_create_url('core/modules/ckeditor/css/ckeditor-iframe.css'),
       file_create_url('core/modules/system/css/components/align.module.css'),
-      file_create_url('core/modules/ckeditor/css/plugins/language/ckeditor.language.css'),
     );
   }