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 27a32ae..62d66d1 100644
--- a/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/Editor/CKEditor.php
@@ -271,28 +271,35 @@ public function getJSSettings(EditorEntity $editor) {
    *   An associative array keyed by language codes.
    */
   private function getLangcodes() {
+    // Cache the file system based language list calculation because this would
+    // be expensive to calculate all the time. The cache is cleared on core
+    // upgrades which is the only situation the CKEditor file listing should
+    // change.
     $langcodes = cache('ckeditor')->get('langcodes');
     if (empty($langcodes)) {
       $langcodes = array();
       // Collect languages included with CKEditor based on file listing.
       $ckeditor_languages = glob(DRUPAL_ROOT . '/core/assets/vendor/ckeditor/lang/*.js');
-      // Get language mapping if available to map to Drupal language codes.
-      $language_mappings = $this->moduleHandler()->moduleExists('language') ? language_get_browser_drupal_langcode_mappings() : array();
       foreach ($ckeditor_languages as $language_filename) {
         $langcode = basename($language_filename);
         $langcodes[$langcode] = $langcode;
-        // If this language code is available in a Drupal mapping, use that
-        // to compute a possibility for matching from the Drupal langcode to
-        // the CKEditor langcode.
-        if (isset($language_mappings[$langcode]) && !isset($langcodes[$language_mappings[$langcode]])) {
-          $langcodes[$language_mappings[$langcode]] = $langcode;
-        }
       }
-      // @todo figure out when should this be cleared. With the current code
-      // this would need to be cleared on browser mapping changes and core
-      // updates. That sounds like too much outside interference(?).
       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.
+    $language_mappings = $this->moduleHandler()->moduleExists('language') ? language_get_browser_drupal_langcode_mappings() : array();
+    foreach($langcodes as $langcode) {
+      // If this language code is available in a Drupal mapping, use that
+      // to compute a possibility for matching from the Drupal langcode to
+      // the CKEditor langcode.
+      if (isset($language_mappings[$langcode]) && !isset($langcodes[$language_mappings[$langcode]])) {
+        $langcodes[$language_mappings[$langcode]] = $langcode;
+      }
+    }
+
     return $langcodes;
   }