There are 11 official languages and a few more unofficial ones, so there are lots of ways.
Many people Speak English as a second language in South Africa (only 8% speak it as a first language), but it also goes without say that South Africans enjoy the little time and effort it takes to greet them in their home language. See related links for a good resource we use in class.
Here is the list of "hi" in the 11 official languages of South Africa:
English Hello, Hi
Sesotho sa Leboa Dumela
Tshivenḓa ♂Ndaa / ♀Aa
Xitsonga Avuxeni (pronounced Avoo-sh-eni)