Mein Anrate: Lernen Sie spanisch, wenn du einer Deutscher spielen wollen. In die letze Tage meine Deutscherin Leben ich sprach nur spanische Leute mit...
That and I don't have much time to finish learning German anymore.

Hard enough at the moment to maintain an English character and a Finnish character with the bare minimum input needed for the game right now.
Having played character in five language groups now, and only one in a language that I had absolutely no proficiency in, I have to follow the advice given by Sanchez and Alf. You can do it, but you'll have to be dedicated to actually learning the words.
Being text based, it's hard to keep yourself oriented if you're not actively imagining the items in your inventory. You can't even tell if people are looking at you...it's a very isolating experience. It does illustrate just how important non-verbal communication can be, though, so as a learning experience it would be worth it there.
What ever you do, don't just talk through the translator. If you're going to talk, learn the language. My approach, if you really really wanted to attempt it, is to play a retard learning to survive in society. There are still a handful of role players out there that will find it entertaining and take the time to interact with you and try to teach you words and stuff.
My silly little Polish guy made it to his forties that way before he finally lost the will to keep living.
"Y-O-U! It's just two extra letters! Come on, people! This is the internet, not a barn!" --Kid President