Can you effectively supervise a person operating in a language you do not understand?. .. .In practice, the problem may not be especially significant even if operating at small GA fields: French GA pilots seem to show commendable restraint on the RT: ie they are not always chattering on it like we are, and often just a few blind position calls, in French, on the standard frequency will do (that Robin your wife just heard reporting vent-arriere is at another airfield fifty miles away). There is a list of the standard calls on the higher-flyer website, and in the Pooleys Delage.. .. .Still, no harm in you learning some French, or your wife getting an RT licence.