diff -u b/core/lib/Drupal/Core/Entity/EntityFormController.php b/core/lib/Drupal/Core/Entity/EntityFormController.php
--- b/core/lib/Drupal/Core/Entity/EntityFormController.php
+++ b/core/lib/Drupal/Core/Entity/EntityFormController.php
@@ -430,9 +430,9 @@
    * Updates the form language to reflect any change to the entity language.
    *
    * @param array $form_state
-   *   A keyed array containing the current state of the form.
+   *   A reference to a keyed array containing the current state of the form.
    */
-  protected function updateFormLangcode(array $form_state) {
+  protected function updateFormLangcode(array &$form_state) {
     // Update the form language as it might have changed.
     if (isset($form_state['values']['langcode']) && $this->isDefaultFormLangcode($form_state)) {
       $form_state['langcode'] = $form_state['values']['langcode'];