If you want to operate in Africa the best languages to learn are English, French, Arabic, and Portuguese.
Most countries have one or the other of these as their legal and official language, and most people in the cities speak one of these languages, depending on which country.
Great point.
The tribal languages that Africans speak among their kinsmen and families are insular and not understood with as much geographical reach as the language of whatever colonial power occupied their region, such as English, French, Portuguese, etc.
In most parts it's advantageous also to learn Swahili, since everyone knows it. It was the language invented jointly by the Arab slave traders and their tribal suppliers and customers.