Article 100-5 of the French Code of Criminal Procedure
The investigating judge, the judicial police officer assigned by him or her, or the judicial police officer or investigative assistant acting under the control of that officer, shall transcribe correspondence that is useful in ascertaining the truth. This transcription is placed in the file. Correspondence in a foreign language is transcribed into French with the assistance of an interpreter requested for this purpose. On pain of nullity, correspondence with a…