Polish language is the official language in criminal proceedings in Polish courts of law. If a person who does not know Polish takes part in the proceedings, and there is a need to question them, a translator must be summoned.

The only criteria that determines the obligation of summoning a translator for a person is the level of proficiency in Polish language of that person. The obligation of appointing a translator is independent of the character in which the person is to be questioned. It is irrelevant whether it concerns the defendant or witness. A translator must also be summoned if there is a need of translating into Polish a document made in a foreign language, or the other way round, or to acquaint the litigant with the content of the evidence taken.

A translator is a proxy to the court, owing to whom this organ can communicate with a person being questioned or to become acquainted with the content of a document. 

A translator must have translation skills from Polish to the foreign language or from the foreign language to Polish. For example, if the witness in proceedings is a person who does not speak Polish. In such a case, a translator is appointed who translates into Polish what the witness says, or translates all the questions into the language the witness speaks.

A translator must be appointed when there is a need of questioning a deaf or mute person, and written communication is not enough. It's vital to highlight that a witness does not cover any costs connected with the participation of a translator.