The exact number of Swahili speakers, be it native or second-language speakers, is unknown and a matter of debate. Various estimates have been put forward and they vary widely, from 50 million to over 100 million. Swahili serves as a national language of four nations: Tanzania, Kenya, Uganda, and the DRC. Shikomor, the official language in Comoros and also spoken in Mayotte (Shimaore), is related to Swahili. Swahili is also one of the working languages of the African Union and officially recognised as a lingua franca of the East African Community.South Africa legalized the teaching of Swahili in South African schools as an optional subject beginning in 2020.
A significant fraction of Swahili vocabulary derives from Arabic, in part conveyed by Arabic-speaking Muslim inhabitants. For example, the Swahili word for "book" is kitabu, traceable back to the Arabic word كتابkitābu (from the rootk-t-b "write"). However, the Swahili plural form of this word ("books") is vitabu, following Bantu grammar in which ki- is reanalysed as a nominal class prefix, whose plural is vi-.