Is it possible to study too many things in parallel?
Actually, what you want to do is commendable. And no, at the scale of things you talk about, I don't think you are likely to get yourself confused. In fact, you may have the opportunity to learn different things in an integrated way. In some ways the educational system, which puts different topics in different boxes, isn't optimal and everyone needs some experience in integrating what they know into a personal whole. 

I once learned quite a bit of French by reading Math papers from French mathematicians, though I was already pretty good at math, but you could, for example, read CS papers in Russian. Knowing something of the underlying ideas before you start lets you focus on how they are expressed in Russian, rather than Japanese or English. 

You already seem to be aware that you will need discipline and to set aside time for your studies. That works for nearly everyone. If you are studying several things then you can also switch to something else at a point at which you either get stuck on some idea, or get tired of the current topic. Often letting your mind work on something else is a good way to let your unconscious work out details that you might miss when working in a concentrated way. 

You should also be aware that you are now (age 20) at the height of your mental (as well as physical) powers. It is never too late to start, but you are starting at a good point. Onward.