Making FinishResponseSubscriber dependent on the language_manager service

core/lib/Drupal/Core/CoreBundle.php

@@ -55,6 +55,8 @@ public function build(ContainerBuilder $container) {
     $container->register('legacy_controller_subscriber', 'Drupal\Core\EventSubscriber\LegacyControllerSubscriber')
       ->addTag('kernel.event_subscriber');
     $container->register('finish_response_subscriber', 'Drupal\Core\EventSubscriber\FinishResponseSubscriber')
+      ->addArgument(new Reference('language_manager'))
+      ->setScope('request')
       ->addTag('kernel.event_subscriber');
     $container->register('request_close_subscriber', 'Drupal\Core\EventSubscriber\RequestCloseSubscriber')
       ->addTag('kernel.event_subscriber');

core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php

@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\EventSubscriber;
 
+use Drupal\Core\Language\LanguageManager;
 use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
 use Symfony\Component\HttpKernel\KernelEvents;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
@@ -16,6 +17,12 @@
  */
 class FinishResponseSubscriber implements EventSubscriberInterface {
 
+  private $language_manager;
+
+  public function __construct(LanguageManager $language_manager) {
+    $this->language_manager = $language_manager;
+  }
+
   /**
    * Sets extra headers on successful responses.
    *
@@ -30,7 +37,7 @@ public function onRespond(FilterResponseEvent $event) {
     $response->headers->set('X-UA-Compatible', 'IE=edge,chrome=1', false);
 
     // Set the Content-language header.
-    $response->headers->set('Content-language', language_manager(LANGUAGE_TYPE_INTERFACE)->langcode);
+    $response->headers->set('Content-language', $this->language_manager->getLanguage(LANGUAGE_TYPE_INTERFACE)->langcode);
 
     // Because pages are highly dynamic, set the last-modified time to now
     // since the page is in fact being regenerated right now.

core/lib/Drupal/Core/Language/LanguageManager.php

@@ -10,8 +10,12 @@
 use Symfony\Component\HttpFoundation\Request;
 
 /**
- * The LanguageManager service intializes the language types passing in the
- * Request object, which can then be used for e.g. url-based language negotiation.
+ * Class responsible for initializing each language type.
+ *
+ * This service is dependent on the 'request' service and can therefore pass the
+ * Request object to the code that deals with each particular language type.
+ * This means the Request can be used directly for things like url-based language
+ * negotiation.
  */
 class LanguageManager {