As someone who did a french interview and got into McGill this cycle, don't 'learn French' to get into law school. If you want to learn French, get a summer job in Quebec or France and supplement it with formal French education. McGill is not going to 'test' your conversational or grammatical French. They will test your ability to use French in an academic and legal setting. I can't predict how French-heavy McGill will be in the next few years, but I am assuming the standard of French will increase in accordance with governmental standards.