South Africa has eleven official languages. Almost all official communication such as road signs and media are in English. Afrikanns and Zulu are also widely spoken  Here are some phrases and words that you can try and impress the locals with:

Some Zulu
Sawubona (sow-oo-born-a) - Hello
Ngikhona wena? (gi-corner-when-a) - I'm fine and you? 
Sharp! (Shup!) - Great!  
Yebo ( Yeah-bor) - (Yes) 
Ngi-ngu Mark (Ingi-ingoo) - My name is Mark.   
Hawu! (How!) - Gosh!
Hambakahle (hum-ba-guy-ller) - Go well, good-bye 

Some Afrikaans
Goeie dag  - Good day
Hoe gaan dit? -How are you?
Goed - Fine
Ja - Yes
Aseblief - Please
Nee dankie - No thanks 
Tot siens - Bye

South African Slang
Lekker means "nice." ie: I had a lekker time today. 
Howzit? means "Hi, how are you?"
Shame means "Cute, delightful..." ie: Look at the little puppy. Shame! 
Braai means "Barbecue" 
Bakkie means pick up truck. (Pronounced "bucky")
Just now means "quite soon." ie: I'll be ready to go just now. 
Now now means "very soon" ie: Don't panic, I'll be there now now.