After a review of the five major areas in which forensic linguistic research is active, this paper examines in particular the notion of linguistic disadvantage as it has evolved in France. The importance of linguistic disadvantage is related to the inquest method of legal procedure, and grew with the increased power of the king’s law, as opposed to local customary law. The king’s language spread with the king’s justice, even as new conquests and acquisitions gave the king dominion over more regions that spoke languages other than French. After the French Revolution, the policy of equality through linguistic uniformity steadily reduced the number of non-French-speakers, and the linguistic disadvantage of many French citizens. This paper examines the use of interpreters and translators in the court system, and also the requirements relating to the registration of names for newborns. The dearth of research on forensic linguistics in the Francophone world makes this a particularly fertile field for the future.