[Routing] i18n routing

[javiereguiluz]

Lots of config examples here: symfony/symfony#26143

Instead of adding this to normal routing docs, it may be better to create a separate article for this feature? Maybe not ... the explanation can be really concise. Let's think about this.

[dominikhajduk]

proposal: #9510 but as there are a lot of examples maybe separate page will be better?

[javiereguiluz]

Fixed by #9515.