What language does the first text go out in, since the call never spoke?

Good question, honest answer: a missed call doesn't announce its language, so the first text goes out in your line's default — usually the language of your business and area. From the first reply, the detected language takes over and the whole exchange switches if needed. You can also set a language per line if your campaigns target different communities. French and English are both native; if your area is mostly anglophone, set English as default and French will follow the reply.