Once you have determined a need for an interpreter and you've actually gone ahead and appointed a qualified interpreter, then it's your responsibility as a judge to actively supervise the interpretation. What you're going to have to do basically is you're going to have to listen with both your ears and your eyes. So that, for example, if a defendant has the benefit of an interpreter, and if a witness is testifying, but you notice because you're observing that the interpreter is actually not simultaneously interpreting, the interpreter is not interpreting what the question is, or even what the answer is, then you have an obligation as a judge to stop the proceedings and inquire why it is that the interpreter is actually not interpreting each question and each answer given by the witness.
So that's what I mean that you have to listen with your eyes as well. You might have another situation where you have a witness who is testifying, who does not speak English and has an interpreter. But let's say the witness is describing injuries that they suffered and they talk about having headaches, they talk about neck pain, they talk about stomach pain, and they indicate physically where else they are experiencing pain, but the interpreter says, the witness says that he only experiences headaches, then you know based on your observations, because the individual is touching other parts of their anatomy, that there's probably a question whether or not the interpreter is actually accurately interpreting.
So look for silence when simultaneous interpretation is required. Make sure that the response that the interpreter is giving is consistent with some of the physical motions of the witness or the litigants.