In my experience, Swahili wasn't widely spoken, really only in a region of East Africa around Uganda/Kenya/Tanzania - which I also realized many foreigners come to think of as "Africa" because that's where they go on safari. It was great to drive from Tanzania into Burundi, or Ethiopia into Djibouti and not see a single foreigner for a month.
Certainly French is the language of the West Coast and of many hundreds of millions of people. I'm guessing if it also had Nigeria's 200million it would be the dominant language on the continent.
English, again, is common in the places tourists frequent, but otherwise not widespread outside the capital cities.
The vast majority of people even in very, very remote mud hut communities spoke at least two languages. 3+ was very common.