Alternative Languages

To anyone from St. Petersburg or who has been there,

Which alternative language would be better for me to have a basic concept of in that city? French or German? Obviously Russian is the best, and I can speak, read, and write Russian pretty well. But there come some times when I can't think of how to express a thought in Russian. I can speak some German, but I'm not sure if French as a second language would be more common than German or vice versa. Which would people be more likely to know?

Thanks in advance