What do French police say when arresting someone in France?

There is no "Miranda warning" formula or similar thing to be read to the arrested person. Police officiers give the information they want at the time of the arrest, usually something along the line of "we're going to sort that matter out at the station". When back at the police station, the arrested person will be interviewed by a detective who will inform him that he is under police custody and inform him of his legal rights (have someone informed of his arrest, see a lawyer, a medical doctor, etc..) before proceeding with the interview on the facts.