Symfony 7 impossible translation

Question

I'm working on an end-of-course project with a group of colleagues on Symfony 7. I created two files messages.en.yaml and messages.fr.yaml in which I created all the language variables, translated them and installed them throughout the backoffice. I'd like to switch from one language to another at the click of a button. But it doesn't work. If I add /{_locale}/ to the paths in my controllers and in the url, I see that my translations work. If I dump and die in my languageController, I also find the values of the locale. But the buttons don't work, there's no automation.

I read the symfony doc, chatted with chatGTP — none of the things I read worked. Nor did my trainers' or colleagues' attempts. I've tried so many things that I can't remember any of them. What I do remember doing is composer require symfony/translation. Then I followed the docs and used chatGTP to come up with a rough rendering of the files I'm attaching.

Here's my translation.yaml:

framework:
    default_locale: 'en'
    translator:
        default_path: '%kernel.project_dir%/translations'

Here's my routes.yaml:

controllers:
    resource:
        path: ../src/Controller/
        namespace: App\Controller
    type: attribute

api_login_check:
    path: /api/login_check

app.swagger_ui:
    path: /api/doc
    methods: GET
    defaults: { _controller: nelmio_api_doc.controller.swagger_ui }

switch_language:
    path: '/{_locale}/'
    controller: 'App\Controller\LanguageController::switchLanguage'
    requirements:
        _locale: 'en|fr'

Here's my language controller:

<?php

namespace App\Controller;

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;

class LanguageController extends AbstractController
{
    #[Route('/{_locale}/switch-language', name: 'switch_language')]
    public function switchLanguage(Request $request, $_locale): Response
    {
        $request->getSession()->set('_locale', $_locale);
        return $this->redirect($request->headers->get('referer'));
    }
}

And here are my buttons supposed to switch languages:

<!-- Language Switching Links within the navbar -->
                        {% if app.request.locale != 'en' %}
                            <li class="nav-item">
                                <a class="nav-link" href="{{ path('switch_language', {'_locale': 'en'}) }}">{{ 'English'|trans }}</a>
                            </li>
                        {% endif %}
                        {% if app.request.locale != 'fr' %}
                            <li class="nav-item">
                                <a class="nav-link" href="{{ path('switch_language', {'_locale': 'fr'}) }}">{{ 'French'|trans }}</a>
                            </li>
                        {% endif %}

I've only been coding for six months, so it's particularly tricky. So I'd be grateful for anyone's help.