Language Family

Most of the languages spoken in Sub-Saharan Africa fall into the Niger-Kordofanian or Niger-Congo language family. The vast majority of the languages in that family are in the Bantu subfamily, and are called Bantu languages. This language family includes languages in East Africa such as Kikuyu and Swahili, and languages in Central Africa such as Kikongo and Lingala. Xhosa, as well as most of the languages of South Africa, are also in this Bantu language subfamily, and while Xhosa is distantly related to languages like Lingala and Swahili, it is very closely related to Zulu, Swati, and Ndebele (just as English is distantly related to Russian but more closely related to Dutch). In fact, Xhosa, Zulu, Swati and Ndebele are referred to as the Nguni languages, and are often (but not always) mutually intelligible. For example, consider how you say "I love you" in the following languages:

Xhosa	Ndiyakuthanda
Zulu	Ngiyakuthanda
Sotho	Ke a go rata
Swahili	Ninapenda wewe

As you can see, Xhosa and Zulu are very close, whereas it would take you a little more research to see how Sotho and Xhosa are related (and a lot more to make the connection between Swahili and Xhosa).

While Xhosa is considered a bantu language, the "clicks" in Xhosa actually come from another source. When bantu language speakers migrated to South Africa, they encountered the Khoisan people, and over time, they adopted some of the clicks that the various Khoisan people use in their languages. Unfortunately, most of the Khoisan languages are slowly dying out,and the largest Khoisan language, Nama, has only about 250,000 speakers.