You really think that rural folks in most of Sub-Saharan Africa go to school?
And the vernaculars change almost from village to village.
To come closer to home, Mexico has over 100 languages and dialects. There are quite a few parts of rural Mexico where most people don't even speak Spanish as a second language and the children work in farming and other "trades" from the time they are 6 or 7.
And that is just in Mexico. In Ecuador I had to learn the regional dialect of Quechua back in the 60's as the people who watched my transmitter sites would revert to that tongue if there was a lightening hit or sparks "in the box".
The understanding of the educational levels and language abilities of people in such areas is not very good here in the U.S.A.
If they are urban and somewhat educated.
And there are many other languages. My first hit on "languages of Sub-Saharan Africa got this from our friend, the renowned linguist, Mr. A. Intelligence:
Popular to the sub-Saharan region of Africa are languages such as Swahili, Hausa, Yoruba, Igbo, Wolof, Amharic, Shona, Oromo, Kongo, Lingala, Zulu, and so on. These languages are divided into major language families. These families are Bantu, Indo-European, Niger-Congo, and Austronesian
A deeper search reveals
At least 1.34 billion people inhabit Africa. Eighty-one percent, which is 1.09 billion, of this population, are inhabitants of Sub-Saharan Africa. There are no less than a thousand languages among countries that belong to this region. Given that the citizens of Nigeria alone (a country in Sub-Saharan Africa) speak over 500 languages, allocating just a thousand languages to the region is believed to be a gross devaluation.
So there you go... 500 languages just in Nigeria.
Before the pandemic, I was working on a project in Bolivia that mimicked some of the cellular phone "banking" developed in Africa. Using an app, people could even buy vegetables from street vendors or receive payment for random incidental jobs. Our idea was to create such a service in Bolivia but tie in over a dozen radio formats in at least 3 or 4 languages where advertisers would reach consumers directly on the radio "stations" and the consumers would seek out products anywhere and buy them using product codes for discounts run with the radio ads.
Our investigations in a variety of African nations showed that for most people Spanish was not the first language for effective messaging. But one side benefit is that the mobile devices could be used to translate dynamically for buyers and sellers of different cultural groups.