Well, let me start by making it clear that Nigeria and Ethiopia had quite very much differences in our colonial histories. Ethiopia as a multi-ethnic state was never really ruled for long by the Europeans or brought together as one nation by the Europeans hence the use of a single native language as the official language in spite of the ethnic diversity. In the case of Nigeria, Hausa language was successfully promoted to be the lingua franca and supposedly official language of the Northern region of the country which had hundreds of ethnic groups. It worked and that's why till date Hausa has more 2nd language speakers than native speakers in Nigeria. Promoting Igbo & Yoruba as the unifying languages of the South somehow failed because the British somehow preferred the South divided so that the north could dominate and rule the entire country as the British were very pleased at the powerful monarchial system of government and literacy they met in northern Nigeria. The northern...