[HttpKernel] fix sending Vary: Accept-Language when appropriate

Author: nicolas-grekas

src/Symfony/Component/HttpKernel/EventListener/LocaleListener.php

@@ -70,6 +70,7 @@ private function setLocale(Request $request)
             $request->setLocale($locale);
         } elseif ($this->useAcceptLanguageHeader && $this->enabledLocales && ($preferredLanguage = $request->getPreferredLanguage($this->enabledLocales))) {
             $request->setLocale($preferredLanguage);
+            $request->attributes->set('_vary_by_language', true);
         }
     }
 

src/Symfony/Component/HttpKernel/EventListener/ResponseListener.php

@@ -50,6 +50,9 @@ public function onKernelResponse(ResponseEvent $event)
 
         if ($this->addContentLanguageHeader && !$response->isInformational() && !$response->isEmpty() && !$response->headers->has('Content-Language')) {
             $response->headers->set('Content-Language', $event->getRequest()->getLocale());
+        }
+
+        if ($event->getRequest()->attributes->get('_vary_by_language')) {
             $response->setVary('Accept-Language', false);
         }