Self-study language

So, I'm thinking about starting a selfstudy language in january, mostly to give me something to do (I have a lot of free time) and also because I'm curious to see how far I could come.

I already speak/understand a few languages(English, German, French, Dutch, Latin, Greek) and am currently majoring in Japanese. My preference would be an asian language but that might become a bit much with me studying Japanese at the same time. Another language I considered was Swedish due to it's easy nature (for those that already know some Germanic languages) but what's keeping me from it atm is the uselessness of understanding Swedish.

Any tips/recommendations for languages that are suitable for selfstudy?

OP is asking for tips on how to learn a language by himself, not which language to learn but tips on how to learn one.

OP check out http://how-to-learn-any-language.com/forum/ has a lot of info in it about languages and learning them.