Will this look bad for NYU/USC/UCLA?

My advice would be to sit for the foreign language AP exams you mentioned even if you don't take the class. Still, it probably won't look great to only have 3 credits in most of your core subjects. I'd recommend taking at least one class over the summer or doing something really interesting while your abroad instead of just "studying" for no credit. Even if you work like crazy, no grades and no test scores are going to make it look like you just spent a year having a good time.