Symfony version(s) affected: All

Description

When using internationalized routes with _locale as a prefix, the UrlGenerator creates routes with the correct route name but the wrong _locale.

For example:

When there are two routes available:

en: /bug
de: /fehler

Then the CompiledUrlGenerator and UrlGenerator generate /en/fehler for the German route when en is the default locale.

How to reproduce

https://github.com/git-chrisp/symfony-routing-bug

Visit the path /de/fehler. It should show /de/fehler but shows /en/fehler instead as en is the default locale.

This repository is the website skeleton with the following additions:

1. DefaultController with one route
2. The prefix has been configured in config/routes/annotations.yaml
3. One template to show the bug

Possible Solution

In line 59 of the CompiledUrlGenerator (https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Routing/Generator/CompiledUrlGenerator.php):

$parameters['_locale'] = $locale ?? $defaults['_locale'];

Same has to be done in the UrlGenerator: https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Routing/Generator/UrlGenerator.php

Additional context

Please correct me if I'm wrong or my proposed fix doesn't work. Otherwise, I'd gladly create a pull request.