No, I understand that, Stack - I didn't mean that the witnesses must use English what I mean is, the court uses the mother-tongue of the accused - here Pistorius. The witness testimony then must be entered into the court in English. The witness saying it and it being entered into the court are two different things. They can happen simultaneously, but they don't have to.
The witnesses can either choose to speak English, or speak their mother tongue with an interpreter putting it into English. Neither is a perfect situation, because there are nuances in languages that don't carry across. There is no English word for Schadenfreude for example. The nearest would be to say 'he was upset, and I was happy about that' which isn't the same exactly. I seem to remember that the man speaking Zulu explained that in Zulu there is the word for a 'scream' and the word for 'a sort of shouted scream' and a word for 'shout'. We don't have that middle one.
The reason it's 'fair' is that the accused ought to be able to understand what's being said, but it does mean that there will be issues with interpretation.
(I've just got to the part where Roux is reading Stipp's testimony to Burger. He translated it and shortened it at Nel objected. The Judge told him he must read it in Afrikaans, and then the court translate would translate. It struck me as an odd situation where an Afrikaans speaking person would read an Afrikaans written statement to an Afrikaans Mother tongue person in English, then question her in English, and she would answer in English/Afrikaans for the benefit of the court.
The judge is clearly more experienced in dealing with this and cut to; read it in Afrikaans, and we'll translate officially. The lawyer, the witness will hear it in Afrikaans which is better, but for the court's benefit, there will follow a translation.)