Contributed by Kevin Bond
in #45793.

Working with the locale in Symfony applications is simple. The locale is stored
in a request attribute called _locale and used in the rest of the application.
Changing the locale (e.g. in multilingual applications via a list of languages
selectable by users) requires changing that request attribute in an early event listener.
However, sometimes you need to change the locale of the application dynamically
just to run some code. Imagine an application that renders Twig templates of
emails in different languages. You need to change the locale only to render those
templates.
In Symfony 6.1 we're improving situations like this thanks to a new locale switcher.
The LocaleSwitcher object/service allows you to change at once the locale of
all the services that are tagged with kernel.locale_aware.

use Symfony\Component\Translation\LocaleSwitcher;

class SomeClass
{
public function __construct(
private LocaleSwitcher $localeSwitcher,
) {}

public function someMethod()
{
// you can get the current application locale like this:
$currentLocale = $this->localeSwitcher->getLocale();

// you can set the locale for the entire application like this:
// (from now on, the application will use 'fr' (French) as the
// locale; including the default locale used to translate Twig templates)
$this->localeSwitcher->setLocale('fr');

// you can also run some code with a certain locale, without
// changing the locale for the rest of the application
$this->localeSwitcher->runWithLocale('es', function() {

// e.g. render here some Twig templates using 'es' (Spanish) locale

});

// ...
}
}

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