You have the right to an interpreter in court if you need one to make yourself understood.
Section 14 of the Canadian Charter of Rights and Freedoms guarantees a person's right to an interpreter (whether the person is an accused or a witness) if they do not speak or understand the language being used or if they have difficulty making themselves understood in that language.
You should always tell your lawyer, the Prosecutor or the judge if you need an interpreter to fully understand and make yourself understood. Lawyers, judges and other court officials are also supposed to ask you about this if they think you might need an interpreter.
There are certain standards that need to be met by an interpreter, including that they be impartial. This means than interpreter cannot generally be a family member or close friend of someone involved in the matter and they cannot be connected to what happened. There are exceptions and it is up to the judge to make sure an interpreter can provide reliable and impartial interpretation. If you do not have confidence in the chosen interpreter's ability to do this, you should say something.
See What is the Cree Court for an example of the court adopting an Indigenous language as the primary language of the court.