The data (as of 2019) focus on L1 languages, i.e., people’s primary languages to make sure we were only including languages that were actually used on a daily basis.
We started out by gathering data from the CIA World Factbook and listed the most commonly used languages in all the countries we could, and then filled in any gaps and double-checked the information with the world language website, Ethnologue.
Whenever any data from Ethnologue didn’t match up with the CIA’s data (as it includes L2 languages as well), we swapped it for the Ethnologue data.
Your source seems to use L2 data for much of Africa. For example, Madagascar's answer should, without doubt, be Malagasy, not French. And there are many more. Why not just use Ethnologue for every country?
The data (as of 2019) focus on L1 languages, i.e., people’s primary languages to make sure we were only including languages that were actually used on a daily basis.
We started out by gathering data from the CIA World Factbook and listed the most commonly used languages in all the countries we could, and then filled in any gaps and double-checked the information with the world language website, Ethnologue.
Whenever any data from Ethnologue didn’t match up with the CIA’s data (as it includes L2 languages as well), we swapped it for the Ethnologue data.