That a nation has a national language is a fairly recent idea. I may be wrong but it appears to me it's not older than the French Revolution in its current form. It works fairly well when applied to Europe's chiefly monolingual nations - Germany has German, France has French, Spain has Spanish and so on. Of course there are notable exceptions like Switzerland and Luxembourg, the trend is Europe is more clear cut than in Africa and Asia.
If existence of multilingual states is an exception in Europe, monolingual nation states are a rarity in Asia and Africa. There are at least 103 languages, 14 recognised languages (official at lower level) and two federal in India. South Africa boasts of 14 official languages. They may be extreme cases on both continents, at the same time, however, they present a situation where the idea of a national language isn't feasible.
I read somewhere it's not uncommon for people in Africa to be fluent in four or five languages. And no one there furrows a brow using them until one of them is raised to the status of a national language. It's only then that divisions arise.
To most people, in Asia and Africa, these different languages are part of their identity. I don't think I will ever talk to my friends in Punjabi or family in Hindi. And there isn't going to be an issue until I am told to exclusively use only one of those. That would mean losing a part of your identity.
Perhaps that explains why almost all of the formerly colonised countries continue to read and write in the respective languages of their former masters, while speaking in Hausa or Hindi.