Symfony user sticky locale - symfony

Question

In the past two days I've been trying to make my custom LocaleSubscriber, a subscriber which is supposed to set user's locale to user's preference or to default.
<?php
namespace App\Event\Subscriber;
use App\Entity\Language;
use Doctrine\ORM\EntityManagerInterface;
use Symfony\Component\HttpFoundation\Session\SessionInterface;
use Symfony\Component\Security\Http\Event\InteractiveLoginEvent;
/**
* Class LocaleSubscriber
* #package App\Event\Subscriber
*/
class LocaleSubscriber
{
/** #var EntityManagerInterface */
private $entityManager;
/** #var SessionInterface */
private $session;
/**
* LocaleSubscriber constructor.
*
* #param EntityManagerInterface $entityManager
* #param SessionInterface $session
*/
public function __construct(EntityManagerInterface $entityManager, SessionInterface $session)
{
$this->entityManager = $entityManager;
$this->session = $session;
}
/** {#inheritdoc} */
public function onInteractiveLogin(InteractiveLoginEvent $event)
{
$request = $event->getRequest();
$user = $event->getAuthenticationToken()->getUser();
if (null !== $user->getLocale()) {
$this->session->set('_locale', $user->getLocale());
$request->setLocale($user->getLocale());
} else {
/** #var Language $language */
$language = $this->entityManager->getRepository(Language::class)->findOneBy(['defaultLang' => true]);
$language = $language->getSlug();
$this->session->set('_locale', $language);
$request->setLocale($language);
}
}
}
I'm trying to do this system because all languages are listed in my database (Language is one of my entities) and I want to make this application easy to maintain and extend for non-technical users.
The problem is that after leaving this method, request's locale is back to en and the new locale is kept only in session.
I've dumped at the end of the function dump($request, $this->session->all()) and both have the same language. Also, the priority in services.yaml is set to 15.
App\Event\Subscriber\LocaleSubscriber:
tags:
- { name: kernel.event_listener, event: security.interactive_login, method: onInteractiveLogin, priority: 15 }
Any idea why is not working? Did someone encountered the same problem? Any examples?