A good challenge. It also raises some doubts, I think. Kinshasa and Algiers are in the same boat here; most people will be able to speak and understand French in those two cities, but it's not their first language.
It can get complicated but DRC uses French formally and in schools whereas Arabic is spoken in Algeria formally. Algiers does have a large French-speaking population but majority speak Arabic whereas in Kinshasa, it is majority French-speaking although many speak Lingala