In my experience, they are looking for proficiency in a second language (which in your case would be French). For the third language, as long as you've begun to learn it and let them know that you plan on continue studying it, you should be ok. You don't have to have complete proficiency of two foreign languages when you apply, just proficiency in one, and "reading knowledge" in the other. As for learning either German or Spanish, I can't advise you because they seem like they'd be equally useful. Also, don't sell yourself short on Russian, you might discover you're interested in that language too.