Was the case law provided in the original answer not sufficient?
The citation from R H Christie & G B Bradfield Christie’s the Law of Contract in South Africa (2011) 6 ed at 329-330 as indicated in the original answer is clear that if a party does not understand the language it is his/her duty to indicate such and make an attempt to have the contract translated, even if such an attempt was simply telling you that she does not understand it.
‘However material the mistake, the mistaken party will not be able to escape from the contract if his mistake was due to his own fault. This principle will apply whether his fault lies in not carrying out the reasonably necessary investigations before committing himself to the contract, that is, failing to do his homework; in not bothering to read the contract before signing; in carelessly misreading one of the terms; in not bothering to have the contract explained to him in a language he can understand; in misinterpreting a clear and unambiguous term, and in fact in any circumstances in which the mistake is due to his own carelessness or inattention, . . . ’
There is only an obligation to have an interpreter when one party indicates that he/she does not understand the language. In South Africa there are 9 official languages. An interpreter is usually required when a party indicates in court proceedings that he can't speak English. But the situation is a bit different in Contract Law because to conclude a contract is a voluntary act. And when you conclude a contract you must indicate you don't understand the contract, otherwise the citation from Christie's The Law of Contract in South Africa will apply.
In terms of the common law principle caveat subscriptor, when an agreement is reduced to writing and signed by the parties, they are bound to its terms as signature signifies assent thereto. Once the contract has been signed, she can't afterwards claim she didn't understand it.
I could not find any case law that places an obligation to have an interpreter translating the terms and provisions of the contract.