i'm learning french, spanish, and portuguese simulataniously. i'm not really having that much trouble, but the only thing that i do is, when i don't know the world in one of them, i just substitute it for one in of the other languages. but that's only when i don't know the word in the other one. and when i switch from one to the other really fast without any time in between i use words from all 3 and get really confused. hahaha. but overall it's going really well.
plus i'll be starting Chinese after I get back from my year abroad in Portugal, and I might learn Italian there, as well as perfect my French and Spanish while I'm there.