I'm y13 and do French, Eng lit and history.
In terms of law, either would be useful - Eng lit teaches you to notice the tiny details in texts and react to them, whilst French teaches you how to communicate, how to read a complex text, and provides you with a very practical skill. I'm going to do a French degree, hopefully, so I'd always recommend French first. However, you should do that one you enjoy most so that you'll study harder and get a better grade, hopefully. Perhaps read the books your college would study and see if you like them? Many are available at least in part online. With French, you also do some analysis of books/ a film, but I'd say that vocab and grammar are more important through the a level as a whole. French as the A level that taught me best how to learn through all the vocab, and it's always nice to be able to improve through listening to, watching and reading a wide variety of material!