English: Welcome
Afrikaans: Welkom
Zulu: Sawubona (used as a greeting, also means "hello")
Xhosa: Molo (same as above)
Sesotho: Dumela (same as above)
Tswana: Dumela (same as above)
Venda: Ndi a kho! (Literally: "I see you!")
Tsonga: N'wai (same as above)
Swati: Ngiyamukeleka (Literally: "You are welcome")
Ndebele: Sawubona (same as Zulu)
For a more general and friendly welcome, you could use:
* "Welcome to South Africa!" (in English)
* "Ahlanani!" (in Xhosa, meaning "Welcome!")
It's always good to try and learn a few basic phrases in the local language. People will appreciate the effort you make!