The Swahili language, is basically of Bantu (African) origin. It has borrowed words from other languages such as Arabic probably as a result of the Swahili people using the Quran written in Arabic for spiritual guidance as Muslims.
As regards the formation of the Swahili culture and language, some scholars attribute these phenomena to the intercourse of African and Asiatic people on the coast of East Africa. The word "Swahili" was used by early Arab visitors to the coast and it means "the coast". Ultimately it came to be applied to the people and the language.
Regarding the history of the Swahili language, the older view linked to the colonial time asserts that the Swahili language originates from Arabs and Persians who moved to the East African coast. Given the fact that only the vocabulary can be associated with these groups but the syntax or grammar of the language is Bantu, this argument has been almost forgotten. It is well known that any language that has to grow and expand its territories ought to absorb some vocabulary from other languages in its way.
A suggestion has been made that Swahili is an old language. The earliest known document recounting the past situation on the East African coast written in the 2nd century AD (in Greek language by anonymous author at Alexandria in Egypt and it is called the Periplus of Erythrean Sea) says that merchants visiting the East African coast at that time from Southern Arabia, used to speak with the natives in their local language and they intermarried with them. Those that suggest that Swahili is an old language point to this early source for the possible antiquity of the Swahili language.
Words from Other Languages
It is an undeniable truth that Arab and Persian cultures had the greatest influence on the Swahili culture and the Swahili language. To demonstrate the contribution of each culture into the Swahili language, take an example of the numbers as they are spoken in Swahili. "moja" = one, "mbili" = two, "tatu" = three, "nne" = four, "tano" = five, "nane" = eight, "kumi" = ten, are all of Bantu origin. On the other hand there is "sita" = six, "saba" = seven and "tisa" = nine, that are borrowed from Arabic. The Arabic word "tisa" actually replaced the Bantu word "kenda" for "nine". In some cases the word "kenda" is still used. The Swahili words, "chai" = tea, "achari" = pickle, "serikali" = government, "diwani" = councillor, "sheha" = village councillor, are some of the words borrowed from Persian bearing testimony to the older connections with Persian merchants.
The Swahili language also absorbed words from the Portuguese who controlled the Swahili coastal towns (c. 1500-1700AD). Some of the words that the Swahili language absorbed from the Portuguese include "leso" (handkerchief), "meza" (table), "gereza" (prison), "pesa" ('peso', money), etc. Swahili bull-fighting, still popular on the Pemba island, is also a Portuguese legacy from that period. The Swahili language also borrowed some words from languages of the later colonial powers on the East African coast - English (British) and German. Swahilized English words include "baiskeli" (bicycle), "basi" (bus), "penseli" (pencil), "mashine" (machine), "koti" (coat), etc. The Swahilized German words include "shule" for school and "hela" for a German coin.
Spread into the Hinterland
For centuries, Swahili remained as the language for the people of the East African coast. Long-time interactions with other people bordering the Indian Ocean spread the Swahili language to distant places such as on the islands of Comoro and Madagascar and even far beyond to South Africa, Oman and United Arab Emirates. Trade and migration from the Swahili coast during the nineteenth-century helped spread the language to the interior of particularly Tanzania. It also reached Uganda, Rwanda, Burundi, Congo, Central African Rebublic, and Mozambique.
Christian missionaries learnt Swahili as the language of communication to spread the Gospel in Eastern Africa. So, the missionaries also helped to spread the language. As a matter of fact the first Swahili-English dictionary was prepared by a missionary. During the colonial time, Swahili was used for communication with the local inhabitants. Hence the colonial administrators pioneered the effort of standardizing the Swahili language. Zanzibar was the epicenter of culture and commerce, therefore colonial administrators selected the dialect of the Zanzibar (Unguja) town as the standard Swahili. The Unguja dialect (Kiunguja) was then used for all formal communication such as in schools, in mass media (newspapers and radio), in books and other publications.
Now Swahili is spoken in many countries of Eastern Africa. For Tanzania, deliberate efforts were made by the independent nation to promote the language (thanks to the efforts of the former head of state, Julius K. Nyerere). Tanzania's special relations with countries of southern Africa was the chief reason behind the spread of Swahili to Zambia, Malawi, South Africa, and other neighbouring countries to the south. Swahili is the national as well as the official language in Tanzania - almost all Tanzanians speak Swahili proficiently and are unified by it. In Kenya, it is the national language, but official correspondence is still conducted in English. In Uganda, the national language is English but Swahili enjoys a large number of speakers especially in the military. As a matter of fact, during the Iddi Amin's rule Swahili was declared the national language of Uganda. However, the declaration has never been seriously observed nor repealed by the successive governments.
Thus, Swahili is the most widely spoken language of eastern Africa and many world institutions have responded to its diaspora. It is one of the languages that feature in some world radio stations such as, the BBC, Radio Cairo (Egypt), the Voice of America (U.S.A.), Radio Deutschewelle (Germany), Radio Moscow International (Russia), Radio Japan International, Radio China International, Radio Sudan, and Radio South Africa. The Swahili language is also making its presence in the art world - in songs, theatres, movies and television programs. For example, the lyrics for the song titled "Liberian girl" by Michael Jackson has Swahili phrases: "Nakupenda pia, nakutaka pia, mpenzi we!" (I love you, and I want you, my dear!). The well-celebrated Disney movie, "The Lion King" features several Swahili words, for example "simba" (lion), "rafiki" (friend), as the names of the characters. The Swahili phrase "hakuna matata" (No troubles or no problems) was also used in that movie.
The promotion of the Swahili language is not only in its use but also deliberate efforts are made throughout the world to include it in education curriculum for higher institutions of learning. It is taught in many parts of the world.