At least they all can fluently speak - and sing - English... ;) Or an inbuild universal translator comes with being a princess like talking animal companions. What if they sang in their native language? Well, of course they do, as Disney songs are traditionally dubbed into the languages the movie is dubbed. So - here’s Disney princesses singing in the language they should.
I’m not really sure why Sleeping Beauty is supposed to be French, as it’s another classical Grimm fairy tale, but whatever. I guess they can’t all be German... ;)