Mo. Rev. Stat. § 540.150: Interpreter — appointment — oath.

Whenever in the opinion of any grand jury it shall be necessary to have an interpreter of the testimony to be given before them by any witnesses, they may appoint such interpreter and permit him to be present in the grand jury room during the hearing of the testimony of such witnesses. The interpreter shall first be sworn by the foreperson not to divulge any of the proceedings before the grand jury or the names of any witnesses. The foreperson shall further swear the interpreter to correctly interpret all questions to the witness and all the witness' answers into English.