The Zulu translation is fine, but Sesotho is spelt with O's in English.

IsiSuthu = Sesotho (it is usually known as this in English, not Sotho language) or Sotho way/culture/language
UmSuthu = a Sotho person

don't get caught between prouncing and and written words,the correct word is Sotho but when prounced it sounds like Su,if we were to go the prouncing way Sotho people word be writting Zulu as Sulu because when they prounce Zulu the say Sulu but as we know there is there is no such word as Sulu(Zulu nation) same case go to Sotho people.

akwande,Jozi

I agree with Jozi. The spellings should reflect the customs of the respective language. Pronunciation is a different matter altogether. So now we have:

English -> Zulu:
Sotho -> Suthu