class LanguageRequestSubscriber

class LanguageRequestSubscriber implements EventSubscriberInterface {
    
    /**
     * The language manager service.
     *
     * @var \Drupal\language\ConfigurableLanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * The language negotiator.
     *
     * @var \Drupal\language\LanguageNegotiatorInterface
     */
    protected $negotiator;
    
    /**
     * The translation service.
     *
     * @var \Drupal\Core\StringTranslation\Translator\TranslatorInterface
     */
    protected $translation;
    
    /**
     * The current active user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $currentUser;
    
    /**
     * Constructs a LanguageRequestSubscriber object.
     *
     * @param \Drupal\language\ConfigurableLanguageManagerInterface $language_manager
     *   The language manager service.
     * @param \Drupal\language\LanguageNegotiatorInterface $negotiator
     *   The language negotiator.
     * @param \Drupal\Core\StringTranslation\Translator\TranslatorInterface $translation
     *   The translation service.
     * @param \Drupal\Core\Session\AccountInterface $current_user
     *   The current active user.
     */
    public function __construct(ConfigurableLanguageManagerInterface $language_manager, LanguageNegotiatorInterface $negotiator, TranslatorInterface $translation, AccountInterface $current_user) {
        $this->languageManager = $language_manager;
        $this->negotiator = $negotiator;
        $this->translation = $translation;
        $this->currentUser = $current_user;
    }
    
    /**
     * Initializes the language manager at the beginning of the request.
     *
     * @param \Symfony\Component\HttpKernel\Event\RequestEvent $event
     *   The Event to process.
     */
    public function onKernelRequestLanguage(RequestEvent $event) {
        if ($event->isMainRequest()) {
            $this->setLanguageOverrides();
        }
    }
    
    /**
     * Initializes config overrides whenever the service container is rebuilt.
     */
    public function onContainerInitializeSubrequestFinished() {
        $this->setLanguageOverrides();
    }
    
    /**
     * Sets the language for config overrides on the language manager.
     */
    private function setLanguageOverrides() {
        $this->negotiator
            ->setCurrentUser($this->currentUser);
        if ($this->languageManager instanceof ConfigurableLanguageManagerInterface) {
            $this->languageManager
                ->setNegotiator($this->negotiator);
            $this->languageManager
                ->setConfigOverrideLanguage($this->languageManager
                ->getCurrentLanguage());
        }
        // After the language manager has initialized, set the default langcode for
        // the string translations.
        $langcode = $this->languageManager
            ->getCurrentLanguage()
            ->getId();
        $this->translation
            ->setDefaultLangcode($langcode);
    }
    
    /**
     * Registers the methods in this class that should be listeners.
     *
     * @return array
     *   An array of event listener definitions.
     */
    public static function getSubscribedEvents() : array {
        $events[KernelEvents::REQUEST][] = [
            'onKernelRequestLanguage',
            255,
        ];
        $events[DrupalKernelInterface::CONTAINER_INITIALIZE_SUBREQUEST_FINISHED][] = [
            'onContainerInitializeSubrequestFinished',
            255,
        ];
        return $events;
    }

}