Well, if it‘s any consolation, Fritz‘ brother signed himself „Henri“, too, like Fritz signed himself „Frederic“. Whereas Katte‘s dad, while of course being fluent in French like the rest of the nobility, definitely signed himself Hans Heinrich.

Re: translation of names, I learned about, say, Heinrich VIII (Tudor), Karl I (Stuart) or Franz I (Francois Premier de France, not Leopold‘s kid) in school, don‘t know whether they changed this by now. The only names that didn‘t get adapted from their own language were Italian ones, so Lorenzo de‘ Medici, not Lorenz.