How you might go about determining whether or not an individual, whether actually they are self-represented or a witness or even a juror is, if you detect that English is not their primary language and there's any number of clues that will be available to you, then you should ask the individual some open ended questions about their preferred language, what they normally speak at home, their education level with the English language, things of that nature.

And if you detect from their answers to your questions that the individual does not, is not proficient with the English language then you should go ahead and err on the side of appointing an interpreter for them.

Rules 1-103(B)(5) and 5-122(B)(5) Court must appoint an interpreter if the court perceives the need for an interpreter.