South Africa has 11 national languages, but you can get by with English nearly everywhere. Most white South Africans speak only English or Afrikaans (related to Dutch), while many black South Africans will speak one or more local African languages, plus English, Afrikaans or both. isiZulu and isiXhosa are the two most spoken first languages. About 40% of the population speaks one or other as their mother tongue.
On the whole, English is more widely spoken along the coast and Afrikaans more common inland. All non-native English speakers will appreciate a few words in their home language and you’ll get a big smile if you’re willing to make the effort.