I will be following the book A First Kafir Course by C. J. Crawshaw. The term “Kafir” is certainly NOT the best to refer to either the language or its speakers, but it is a rather old book (I found only the 5th edition printed in 1903), so the use of the term is understandable. Anyway, despite the title,  the book seems to be good, and the language seems to be basically the same as it is used today, as far as I could check.