Perhaps a large concentration of connecting passengers? I think the manifest lists connections so I'm guessing if you had a YHZ-YYZ flight with 30-40 people connecting to AC1 and happened to have a Japanese FA it would be nice to hear a Japanese announcement or some sort of identification that an FA onboard does speak Japanese. It's the little extra touch that makes the difference especially to some cultural groups. I don't think it is mandatory to make announcements in languages other than English/French onboard AC but obviously if it is genuinely going to be appreciated why not? Airlines like AF, EK, and LH often mention they have certain languages represented onboard for passengers who wish to speak in their own language for whatever reason.