You are allowed an interpreter for all stages of select permanent residence applications, including in the immigration interview. Visit the IRCC’s “program-specific procedures for using interpreters” to determine if you will be eligible for an interpreter. If you lack any confidence in your English or French, it is well worth using an interpreter if you are allowed to ensure that you are not misunderstood in the interview.
Having decided that you will use an interpreter, you need to choose one. Many applicants ask for one from the IRCC and will be assigned someone to work with free of charge. However, you can also choose an accredited interpreter if you prefer, but you will have to pay for their services.