It has been a while since I have been to Martinique. I am not sure if the increase in cruise ship traffic has caused an increase in English speakers, but I have heard that, at least in the Fort-de-France area, you can get by. I only was there on sailboats, so I can't help you with roads.

I will suggest that you take a trip to St Pierre. This is where Mt Pelee destroyed the town in 1902. VERY interesting history, and they have preserved walls and buildings that they could. When we visited, the museum interpretation was only in French, but you could get a sense of the destruction from the pictures, etc.

Also, the Ste. Anne area has beautiful beaches.

The food is French, in other words, great. If you can read French menus, you will do fine.