If a person waives the use of an interpreter in court, that person may think that doing so will please the judge and cause him or her to be sympathetic or lighter in sentencing. There is a hesitation, in other words, to accentuate one’s lack of English skills by requesting an interpreter and slowing down the court proceedings, which may upset the judge. What happens when someone waives an interpreter when he or she really does not know English well? The following case summary epitomizes what can go wrong and how an appellate court ruled on the mess.
http://www.greghillassociates.com/the-federal-court-interpreters-act-waiver-of-interpreter.html.