This is an interesting subject. Like Chinua Achebe, my native language is Igbo, and I might be able to speak to it a bit more. Achebe was born in 1930, around the middle of British colonial rule in Nigeria. At that time, English was already established as the language of formal instruction, administration, official transactions, received religion (Christianity), and all things concerning "civilisation". Children grew up speaking their native tongues but those who were privileged enough to go to school then had to learn to speak and write English from childhood.