I haven’t watched the TV show, but from the “bande annonce“, the language seems to be modern. As you observed, the formulations are a tad different, adapted to sound like 1800s.
From the episode, I can clearly affirm that vocabulary is modern French. The sentence formulation could be used as it is in everyday life, but some time it would look “snooty”.
p.s.: You should keep in mind that this language would look a little bit weird in Quebec.
It’s a good modern french language, not familiar. Except if i don’t speak my natif language correctly….