Well, French was the diplomatic language of choice throughout Europe in the 17th-19th centuries, reflecting the predominance of France as well as the huge influence of French thinkers during the Enlightenment. French was the common language of courts and diplomacy; native languages were considered OK for the peasants in Germany, Scandinavia, Russia. Before he began to be older in every book, Jean-Claude appeared to have been born in the late 16th/early 17th century in France, and certainly his upbringing sounds about right for that period,as does the description of the clothing in the now-removed portrait of JC/Asher/Julianna.

I don't know that Hamilton is aware of this, and I agree that a lot of her French terms are very bad translations-like Mort d'Amor for Lover of Death, for instance. Also, Hamilton appears to think of Europe as mostly France, plus possibly sometimes Scandinavian countries or Aryan enclaves somewhere. Germany, Great Britain most of the time, Italy, Spain, the Netherlands, Belgium, Portugal, Greece, the Balkans don't come into it at all.