I think it definitely has limitations. I have been doing French for a few years and have picked up a lot, but still would not be confident speaking it and might struggle to understand it. I ought to watch more videos and TV shows in French, but I treat it as an exercise that may be useful. I started as we were going to French speaking parts of Canada, but did not need it much there. I did learn it at school, but not very well and that was long ago.

I do speak fairly good German as I lived there for a while. I just wonder if learning two similar languages would cause much confusion.