South Africa is a linguistic melting pot. It has 11 official languages, and a smattering of other dialects and creoles that have no official status but are spoken by local communities. In very rural parts of South Africa, many residents speak only the local vernacular. But almost everyone else in this country of more than 50 million people can speak English. English, which is more-or-less politically and ethnically neutral and is the de facto lingua franca (or bridge language) for the entire country. From the beaches of Durban to the wineries of the Western Cape to the grasslands of Kruger National Park, you will be able to get by in English without any problem.
In some areas, local languages may be heard more often on the street (Afrikaans and Xhosa in Cape Town, Zulu in Johannesburg and Durban). However, when two South Africans of different ethnic or linguistic backgrounds communicate, they almost always use English. So not only can you use English to communicate, nearly every South African whom you encounter will expect you to use it.