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Map of languages in West Africa.
(images2.imgbox.com)
The data is quite old, so the number of speakers has probably increased drastically since then. Still, I guess that the proportions and geographical distribution should be more or less the same today.
Cool map! And that Mandingo map is as confusing IRL, lol. In Mali, most people speak at least 2 native languages plus some French, and the dialects or languages can be completely different even 10km apart! We learned Bambara, which was a lingua franca (the irony, haha), but most people in our community spoke Ganakan and Fulakan as well.