They don't have the exactly the same meanings. "do for life" is unnatural. You could replace it with "do for a living" or just "be". In the second, I don't think "chose my career quite naturally" says very much and isn't real smooth. I chose to become ... I naturally fell into being a …. it was a natural choice to become ... What's best would depend on the context. If you aren't going to say what your career is, I think the first sentence (corrected) is better.

Both are okay but personally I would say the first or; I've always been passionate about foreign languages and different cultures, so my career choice came quite naturally to me. Hope that helps:)

Both are correct. In the first sentence it would be natural to say “do in life.”