That's because optional parameters can only be defined at the end of the path. See #5424.

Documentation: http://symfony.com/doc/current/book/routing.html#required-and-optional-placeholders

When just reading the docs, I wouldn't think, that optional parameters only work at the end of a URL. So, maybe this is a docs issue?

Well, then doc is incorrect:
http://symfony.com/doc/current/book/translation.html#book-translation-locale-url

it is indeed incorrect then, let's close this and i have opened symfony/symfony-docs#3450

👍

@MAXakaWIZARD Can you explain why the route /contact can match one of these:

• /en/contact
• /fr/contact
• /de/contact.

IMHO it's weird to have optional placeholder on the path. The doc say:

Unfortunately, this violates a fundamental rule of the Web: that a particular URL returns the same resource regardless of the user. To further muddy the problem, which version of the content would be indexed by search engines?

EDIT after #9981 (comment):
Ho, sorry I don't want to say, the route contact but the path /contact. That's two different things.
So the path /contact cannot match with one of these paths:

• /en/contact
• /fr/contact
• /de/contact

@alquerci It should match, another thing is that you should redirect from /en/contact to /contact, but that's different problem

@MAXakaWIZARD Ho, sorry I don't want to say, the route contact but the path /contact. That's two different things.

It's ok that the route contact should match these paths, to avoid redirection:

• /contact EDIT: without this path
• /en/contact
• /fr/contact
• /de/contact

@alquerci I think if en is default locale, then you anyway should redirect from /en/contact to /contact to avoid content duplication

@MAXakaWIZARD I said really wrong things, sorry for that.

I just wanted to clarify that the doc does not say that the route contact match the path /contact. For do it you need to create an another route who match the path /contact and added the right redirection as you said. Unfortunately this adds code duplication.

There may be another way to do the same thing, like @jakzal said #9981 (comment).

I just wanted to clarify that the doc does not say that the route contact match the path /contact. For do it you need to create an another route who match the path /contact and added the right redirection as you said. Unfortunately this adds code duplication.

This shouldn't be a problem since you can use the RedirectController of the FrameworkBundle in your routing config.

Closing as the actual feature is part of #5424. And the documentation has been updated to clarify the current behavior and confusion that it's not possible yet.

Maybe I solved this in a reasonably simple way:

contact:
    path:      '/{_locale}{_S}contact'
    defaults:  { _controller: 'AppBundle:Example:index' , _locale="de" , _S: "/" }
    requirements:
        _S: "/?"
        _locale: '|de|en|fr'

Curious about the judgement of the critics ...
Best wishes,
Greg

First amendment ...
When you activatie symfony's authentication system and use the login form be sure to use your ROUTES as "*_path"-es (enter the route names there as value, not the virtual path)!