Reading the current locale in Symfony

The locale lives on the Request. In a controller, ask for the request as an argument and read it:

use Symfony\Component\HttpFoundation\Request;

public function index(Request $request): Response
{
    $locale = $request->getLocale();   // 'en', 'fr_FR', ...
}

In a Twig template it is on the app global, with no plumbing at all:

{{ app.request.locale }}

In a service, which has no request argument to take, inject RequestStack:

use Symfony\Component\HttpFoundation\RequestStack;

public function __construct(private RequestStack $requestStack)
{
}

public function currentLocale(): string
{
    return $this->requestStack->getCurrentRequest()?->getLocale() ?? 'en';
}

The null-safe call matters: a service can also run from a console command or a message handler, where there is no current request at all, and getCurrentRequest() returns null rather than inventing one.

Why the old two-liner does not run

$request = $this->get('request');
$locale = $request->getLocale();

$this->get('request') fetched the request as a service. That was deprecated in Symfony 2.4 and removed in 3.0, and the reason is worth knowing rather than just the fact: one shared request object is wrong the moment a sub-request exists. Render a controller from inside a template and there are two requests in flight; a single service can only be one of them. RequestStack replaced it precisely because a stack is what the situation actually is.

$this->get() itself is gone too, removed in Symfony 6.0. A controller does not reach into the container any more; it declares what it needs as an argument or in its constructor.

getLocale() was never the problem and has not changed.

Where the locale gets set

Reading it is the easy half. It is set, in this order, by:

• framework.default_locale in config/packages/framework.yaml, the fallback when nothing else says otherwise;

• a _locale route parameter, which Symfony recognizes specially:

  # config/routes.yaml
  article_show:
      path: /{_locale}/articles/{slug}
      requirements:
          _locale: en|fr|de
  

• $request->setLocale(), usually from a listener that reads a stored preference off the user or a cookie.

A common mistake is calling setLocale() inside a controller and wondering why the translator ignored it — by then the translator has already been handed a locale. Set it in a listener on kernel.request, before the controller runs.