I still don't know what is the best way to sudy a foreign language. Knowing all the rules without being able to speak fluently, or vice versa.
Honestly, I also want to learn another language, and I remember how much fun was to study German (I had an opportunity to study it for a year when Iwas in the university). And I don't think another foreign language will compromize English or Russian for you - it can actually make it clearer how languages work (that's what I remember form my experiences).
Of course, I cannot find a reason to study German now. Though I'd love to.