Cal. Pen. Code § 939.11
Any member of the grand jury who has a hearing, sight, or speech disability may request an interpreter when his or her services are necessary to assist the juror to carry out his or her duties. The request shall be filed with the superior court. If the court, or the judge thereof, finds that an interpreter is necessary, the court shall make an order to that effect and may require by subpoena the attendance of any person before the grand jury as interpreter. If the services of an interpreter are necessary, the court shall instruct the grand jury and the interpreter that the interpreter is not to participate in the jury's deliberations in any manner except to facilitate communication between the disabled juror and the other jurors. The court shall place the interpreter under oath not to disclose any grand jury matters, including the testimony of any witness, statements of any grand juror, or the vote of any grand juror, except in the due course of judicial proceedings.
Ca. Pen. Code § 939.11