from my experience, in term of official languages French is the most spoken official language in Africa(Spoken in 26countries), 2sd : English(20countries), etc. About african dialects, "Swahili" is the most spoken, from Uganda, Kenya, Tanzania, Zanzibar island, Comoros, Rwanda, Burundi, la Somalie, la Zambie, DR. Congo, Congo even in south Africa, you'll find swahili speakers.
Hope my contribution will help you, because I travelled in 11 different African countries, so...good luck in your searches.