It is not something that I have tried doing, but as far as I am aware, you need to be able to open the map in the SC2 Editor so it would need to be unprotected.
Depends on what you want to do. Do you want to take a map, translate it and publish it again (maybe on another server)? Or do you want to help the map creator with his consent to create an official translation (which can be in the same map and it will just show for people using another language).
What you can do is ask the creator to extract the game text for you. You'll get a file with lots of values like Abil/12813/18="This is a tooltip" or such. Then you can translate it and put it back in.
If you don't have the creator's consent to translate it and republish it, it's probably still possible but we can't help you since we don't support map deprotection (See SC2 forum rules)
Well, I'm not planning to translate myself. I just wanted to know if an unprotected map is required for map translation or not. If you can translate it without unprotecting then it's fine.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.