erp5_web: introduce translatable path.

If /help/ Web Section has translation : {'de': 'hilfe', 'fr': 'aide'},
this section can be accessible by the following path :

* /de/hilfe/
* /fr/aide/

Also access to non-translated paths will be redirected like (for GET method) :

* /de/help/* => /de/hilfe/*
* /fr/help/* => /fr/aide/*