Changer le locale dans services.yml

Bonjour à tous j'essaie de faire un site en multilangue histoire d'apprendre la traduction avec symfony.
Tous se passe bien tous marche si je tapre index/en le site est en anglais et si je tapre index/fr le site est en français.
cependant si je dump $request->getLocale() cela me retourne toujours fr même si je suis sur le lien index/en.

Pourquoi la variable locale ne change pas en en ?
Merci

Service.yml:

# This file is the entry point to configure your own services.
# Files in the packages/ subdirectory configure your dependencies.

# Put parameters here that don't need to change on each machine where the app is deployed
# https://symfony.com/doc/current/best_practices/configuration.html#application-related-configuration
parameters:
    locale: 'fr'
    app_locales: en|fr

services:
    # default configuration for services in *this* file
    _defaults:
        autowire: true      # Automatically injects dependencies in your services.
        autoconfigure: true # Automatically registers your services as commands, event subscribers, etc.
        bind:
          $locales: '%app_locales%'
          $defaultLocale: '%locale%'

    # makes classes in src/ available to be used as services
    # this creates a service per class whose id is the fully-qualified class name
    App\:
        resource: '../src/*'
        exclude: '../src/{DependencyInjection,Entity,Migrations,Tests,Kernel.php}'

    # controllers are imported separately to make sure services can be injected
    # as action arguments even if you don't extend any base controller class
    App\Controller\:
        resource: '../src/Controller'
        tags: ['controller.service_arguments']

    # add more service definitions when explicit configuration is needed
    # please note that last definitions always *replace* previous ones
    app.mailer_helper:
      class: App\Service\EmailHelper
      public: true
      arguments:
          - '%env(MAILER_FROM)%'

    App\Service\EmailHelper: '@app.mailer_helper'

    app.exception.listener:
      class: App\Listener\ExceptiontListener
      arguments:
      - '@session.flash_bag'
      - '@router'
      tags:
      - { name: kernel.event_listener, event: kernel.exception, method: onKernelException }

    app.kernel.listener:
      class: App\Listener\KernelRequestListener
      arguments:
        - '@security.helper'
        - '@router'
      tags:
        - { name: kernel.event_listener, event: kernel.request, method: onKernelRequest }

Route de mon controller

@Route("/{_locale}", name="index", defaults={"_locale":"%locale%"}, methods={"GET","POST"})