Dynamically setting a channel's Entry URL Format with Craft tags
I've successfully used this entry url format and it works great:

{{ craft.entries.id(65).first.uri }}/{slug}


I would advise using the entry id over a slug, as it will never change. You also don't need to specify the section if you've included the id.

For a multi-lingual site, you can specify the locale for each entry url format:

{{ craft.entries.id(65).locale('en_us').first.uri }}/{slug}
{{ craft.entries.id(65).locale('de').first.uri }}/{slug}
{{ craft.entries.id(65).locale('fr').first.uri }}/{slug}


As you mention in your comment, you do need to beware of updating the parent entry's slug as uri's are parsed before being stored in the database so it is not truly dynamic. I'm not aware of any workarounds for this that don't involve a plugin.