This is on the accused having a trial in their language, but the witness doesn't speak that language. This provision allows the prosecutor or judge to examine the witness in the witness's own language. This is a very minor amendment to say it's not always automatically done that way--which it doesn't necessarily have to be--and it could prejudice the accused. It adds the words “if the circumstances warrant”.
It was suggested by the witnesses, and it clarifies that the judge can let the witness speak in his own language or one of his own languages if the circumstance is warranted. It makes sure it's not automatic, and if the circumstances warrant, the judge will allow the witness to speak in his own language.