Well, i don't really see the problem with three courses and a language. I am a 1st year PhD student and I took four my first semester and three my second, including working as a teaching assistant in charge of 50+ students and two sections and having a job on the side. The only time that I found it difficult is that end of the semester crunch when final papers are due, but with proper planning you can manage this quite easily. I also did a master's and took five classes at once... I am in history and I do the regular reading load, one book plus a few articles per week per class. Especially if you're not working, I don't see any problem with taking four. I still had a life, went out on the weekends, and got all As in my courses. As long as you plan and budget your time well, you should be just fine.
As for TA assignments, you learn really fast how to cut back on that time. 1) stop assigning writing assignments in addition to the regular assignments. 2) keep the in-class assignments simple and stick to lecture. 3) all those comments you take great pains and time to write? no one reads 'em. Keep it short, brief and to the point. if they have questions, they'll ask you. I know some people have said that students like personal touches but by the 2nd paper I know who will read it and want to think about the comments and who won't.