
Nearly half the 66 million Congolese reportedly speak it, and it is starting to rival Lingala as the most important national language of that country. The five eastern provinces of the DRC are Swahili-speaking. Most educated Kenyans are able to communicate fluently in Swahili since it is a compulsory subject in school from grade one to high school and a distinct academic discipline in many of the public and private universities. Kenya's population is comparable as well, with a greater part of the nation being able to speak Swahili.

Many of the rising generation of Tanzania, however, speak Swahili as a primary language because of a decrease of the traditional cultures and the rise of a more unified culture in urban areas. Some 80 percent of approximately 49 million Tanzanians speak Swahili in addition to their first languages. The neighbouring nation of Uganda made Swahili a required subject in primary schools in 1992. Swahili has become a second language spoken by tens of millions in three African Great Lakes countries (Tanzania, Kenya, and the Democratic Republic of the Congo (DRC)) where it is an official or national language. Today's standard Swahili, the version taught as a second language, is for practical purposes Zanzibar Swahili.

In June 1928, an inter-territorial conference took place at Mombasa, at which the Zanzibar dialect, Kiunguja, was chosen to be the basis for standardising Swahili. One key step in spreading Swahili was to create a standard written language. Another ancient written document dated to 1728 is an epic poem in the Arabic script titled Utendi wa Tambuka (The History of Tambuka). in the Arabic script that were sent to the Portuguese of Mozambique and their local allies. The earliest known documents written in Swahili are letters written in Kilwa in 1711 A.D. It has also incorporated German, Portuguese, English, Hindustani and French words into its vocabulary through contact with empire builders, traders and slavers during the past five centuries.

A significant fraction of Swahili vocabulary is derived from Arabic through contact with Arabic-speaking Muslim inhabitants of the Swahili Coast. Spoken originally along the eastern coast of Africa(the name kiSwahili means 'coastal language'), and now the official language of Tanzania as well as a major language in Kenya, Uganda and the eastern Congo, Swahili is the lingua franca of Eastern Africa.
