.../lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php |   22 ++++++++++++--------
 core/modules/language/config/language.mappings.yml |    3 +++
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
index 335003b..931a45e 100644
--- a/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
@@ -229,14 +229,14 @@ public function getJSSettings(EditorEntity $editor) {
       $settings += $plugin->getConfig($editor);
     }
 
-    // Fallback on English if no matching language code was found.
+    // Fall back on English if no matching language code was found.
     $display_langcode = 'en';
 
-    // Match the interface language code with possible pairs from ckeditor.
+    // Map the interface language code to a CKEditor translation.
     $ckeditor_langcodes = $this->getLangcodes();
     $language_interface = $this->languageManager->getLanguage(Language::TYPE_INTERFACE);
     if (isset($ckeditor_langcodes[$language_interface->id])) {
-      $display_langcode = $language_interface->id;
+      $display_langcode = $ckeditor_langcodes[$language_interface->id];
     }
 
     // Next, set the most fundamental CKEditor settings.
@@ -284,22 +284,26 @@ private function getLangcodes() {
       // Collect languages included with CKEditor based on file listing.
       $ckeditor_languages = glob(DRUPAL_ROOT . '/core/assets/vendor/ckeditor/lang/*.js');
       foreach ($ckeditor_languages as $language_filename) {
-        $langcode = basename($language_filename);
+        $langcode = basename($language_filename, '.js');
         $langcodes[$langcode] = $langcode;
       }
       cache('ckeditor')->set('langcodes', $langcodes);
     }
 
     // Get language mapping if available to map to Drupal language codes.
-    // This is configurable on the user interface and not expensive to get,
-    // so we don't include in the cached language list.
+    // This is configurable in the user interface and not expensive to get, so
+    // we don't include it in the cached language list.
     $language_mappings = $this->moduleHandler->moduleExists('language') ? language_get_browser_drupal_langcode_mappings() : array();
     foreach ($langcodes as $langcode) {
-      // If this language code is available in a Drupal mapping, use that
-      // to compute a possibility for matching from the Drupal langcode to
-      // the CKEditor langcode.
+      // If this language code is available in a Drupal mapping, use that to
+      // compute a possibility for matching from the Drupal langcode to the
+      // CKEditor langcode.
+      // e.g. CKEditor uses the langcode 'no' for Norwegian, Drupal uses 'nb'.
+      // This would then remove the 'no' => 'no' mapping and replace it with
+      // 'nb' => 'no'. Now Drupal knows which CKEditor translation to load.
       if (isset($language_mappings[$langcode]) && !isset($langcodes[$language_mappings[$langcode]])) {
         $langcodes[$language_mappings[$langcode]] = $langcode;
+        unset($langcodes[$langcode]);
       }
     }
 
diff --git a/core/modules/language/config/language.mappings.yml b/core/modules/language/config/language.mappings.yml
index e4ef2a1..ede8c9e 100644
--- a/core/modules/language/config/language.mappings.yml
+++ b/core/modules/language/config/language.mappings.yml
@@ -1,5 +1,8 @@
 # Browsers use different language codes to refer to the same languages,
 # these defaults handles the most common cases.
+no: 'nb' # Norwegian
+pt-pt: 'pt' # Portuguese
+zh: 'zh-hans'
 zh-tw: 'zh-hant' # Taiwan Chinese in traditional script
 zh-hk: 'zh-hant' # Hong Kong Chinese in traditional script
 zh-mo: 'zh-hant' # Macao Chinese in traditional script