Where was the language based on the Boko alphabet primarily used?
Boko alphabet: Boko (or bookoo) is a Latin-script alphabet used to write the Hausa language. Hausa language: Hausa ( ) ("Yaren Hausa" or "Harshen Hausa") is the Chadic language (a branch of the Afroasiatic language family) with the largest number of speakers, spoken as a first language by more than 70 million people, and as a second language by another 40 to 50 million or more. Hausa language:  Originally the language of the Hausa people stretching across southern Niger and northern Nigeria, it has developed into a lingua franca across much of western Africa for purposes of trade.
across much of western Africa