An affidavit is a written statement that you swear is true and that may be used as evidence in a court of law. An affidavit translation is a formal statement sworn under oath.It can also refer to a sworn translation of an official document like a marriage certificate. Both copies will be required in court. Definitions of 'affidavit'. An affidavit is a written statement which you swear is true and which may be used as evidence in a court of law. Paragraph 1: Enter what language other than English you are fluent in. A written statement that someone makes after promising officially to tell the truth. An affidavit can be used as proof in a law court.