Everyone in North America, outside Quebec, thinks that everywhere else in the world, English is the only language spoken on the radio, when in fact that couldn't be further from the truth. In many French African countries (from actual, real-life experience: Gabon, Senegal, Burkina, Mali, Rep. Congo, Cote d'Ivoire, even Morocco and Mauritania) there is quite a bit of French on the airwaves. And in Equatorial Guinea, there's Spanish, French, and even a local language thrown in once in a while, just for extra fun. (English too, but it's ATC's 4th language, usually, so... yeah.)
As far as having French being an advantage over "everyone else" speaking English going to the English African nations - there are a lot of French and Spanish speaking Europeans I've met in French Africa that have a decent amount of flight time but are working for not so great companies & pay in some pretty "interesting" places because they can't find work in Europe. That's not saying you won't be able to find anything, but just another caution not to limit yourself solely based on the perceived lack of competition.
Wherever you go, be careful, watch for scams, question everything, and remember - ass, license, job - in that order. Putting your life on the line every day isn't worth a couple hundred flight hours. If you want to fly in Africa, do it with a Canadian company (Sander, Fugro, Voyageur, Trans Cap, etc etc.)
Good luck.