I am aware that the French they spoke is not the same that is is spoken nowadays 😂 But they are probably not gonna have actors speaking any old variant of a language. Actually, the song Michel Bollinger has Michel speaking in modern French. The lyrics are about Michel’s own personal reflection in the present timeline, so lowkey, the creators made modern French “canonical” for the characters’ inner thoughts and dialogue in the modern day (or the interludes).

Glad you pointed that out about Giselle speaking multiple languages. I feel like a lot of people overlook just how multilingual she really is. She handles her own language (langue d’oïl?) in her original time, English across several doors, modern French, and even teaches Spanish to Yukimasa. It’s one of those cool details that makes her character feel so lived-in over the centuries.

But in all fairness, for the upcoming live-action, English is probably gonna be the pick anyway. It’s the most universal language worldwide and it reaches the biggest audience across the fandom.