Regarding the French language: you don't need to be good at it. Just learn enough of it so you can show the locals you tried, and soon they'll be ok speaking to you in English. All coding languages are English-based so everybody knows enough to work efficiently with non French-speaking people.
Like the other users said, Station F is the flagship startup trend in Paris but there are many startups that don't go there and just operate in Paris itself, it's up to you to find them using meetups (there are plenty) to network.
Coding language wise, it's difficult to say but from my experience a lot of people are into Node.js and Ruby.
Hope this can help, enjoy your time there