Dominica = English Speaking
Guadeloupe = In general no but there are some people who don't speak english or refuse to speak english. I even said good morning in french to a local and they refused to acknowledge = very french
As in any foreign country, speaking the local language or at least trying common phrases is polite & appreciated
We got along just fine even had great laughs trying to talk with some locals who did not speak english - we both tried hard. Any place you want to spend money ie restaurant, marina, bar, etc - will figure it out.
I printed off a bunch of French dictionary words & phrases from the web......used it a few times - it was fun
BUT definitely check the news = the french islands are in turmoil right now