SALEM — A murder trial that promises to be grueling because of the violent way a popular Chinese restaurant owner was killed has been beleaguered by delays due to a lack of Mandarin and Cantonese interpreters to assist the defendants.

Jury selection began Jan. 11 in the trial of Sifa Lee and Cheng Sun, who are charged with murder in the death of Shui Keung “Tony’’ Woo. But the proceedings have been interrupted repeatedly because sometimes no interpreter was available to translate, according to court papers filed Friday by the prosecution.

Lee, 38, requires a Cantonese interpreter and Sun, 51, needs a Mandarin interpreter. Both are charged with first-degree murder in the death of Woo, 62, who was beaten to death on Sept. 27, 2011, inside his Ipswich restaurant, Majestic Dragon. Lee and Sun have pleaded not guilty.

“It’s inexcusable that they don’t have appropriate interpreters to do this whole trial,’’ said attorney John Andrews, who represents Lee.

“The Trial Court had over three months advance notice that these interpreters were going to be needed to try this case and, for whatever bureaucratic reason, they have not been able to supply the necessary qualified interpreters which would have enabled us to impanel a jury by now,’’ he said in a telephone interview.

Essex Assistant District Attorney Kristen Buxton wrote in the court filing that the difficulty of finding interpreters to come to court has added at least two additional weeks to the trial, strained Woo’s relatives, and created problems for witnesses, lawyers, and potential jurors.

The state office that provides interpreters for the court system has only one Cantonese interpreter who is qualified to translate for Lee, Buxton wrote in the filing. That interpreter will not be available on Wednesdays and some other dates during the trial, she wrote.

Two prosecution witnesses also require Cantonese interpreters, including Jun Di Lin, who pleaded guilty in 2014 to manslaughter and other charges in connection with Woo’s death, according to prosecutors.

“We’re in purgatory,’’ Buxton said Friday in Essex Superior Court.

She asked Judge David A. Lowy to order a Cantonese interpreter be retained to come to court on days when the state Office for Court Interpreter Services cannot provide one. Her request specifies the interpreter must be “qualified’’ or “certified,’’ meaning the person must have a certain level of training.

Lowy described the problem as a systemic one in the Trial Court.

“Anything I’ve said about the interpreter shortage in this case is not the fault of the interpreters interpreting the case,’’ he said.

Maria Fournier, the director of interpreter and support services for the court, said her office is working with agencies here and in four other states to hire Mandarin and Cantonese interpreters “who meet the necessary requirements and are available.’’

She said the search has already exhausted local resources, including interpreters who work on a per diem basis or for independent agencies. The office has also asked the US District Court for help, Fournier said.

Attorney Michael T. Phelan, who represents Sun, said the interpreters working on the trial are not state employees but professionals who get offers to provide services to courts as needed. According to its website, the court system has about 175 interpreters, including 24 who are full time.

Interpreters are paid per diem according to their level of training and experience. More highly trained interpreters earn $300 per day or $200 for a half day, according to the form they submit for payment, while less experienced interpreters get $200 for a full day and $125 for a half day.

Phelan said he does not want the trial to be delayed, though he has not had any scheduling problems so far with getting interpreter services for Sun, who speaks Mandarin. A listing of state court interpreters shows there are seven who speak Mandarin and three who speak Cantonese.

Jury selection is scheduled to continue Monday.

Woo’s son, Edwin, said problems scheduling interpreters have beset the case from the onset. “It’s definitely a tough situation,’’ he said.

Laura Crimaldi can be reached at laura.crimaldi@globe.com. Follow her on Twitter @lauracrimaldi.