apparently filmed bilingually

Although I'm not fluent in either language, I'm nearly positive that Pierre Arditi (Blaise) is speaking all his lines in his native French, while most of the other actors are speaking theirs in Italian. Many Italian-made films of this general period relied on post-production dubbing. I wonder if other viewers may have noticed any other actors besides Arditi not speaking Italian.

There's a funny dubbing blooper in chapter 14 where Blaise, on his way to the convent of the Minims to hear Descartes, is accosted by a scandalized man dressed in maroon - at the end of this encounter as Blaise walks away, according to the English subtitles the angry man says "You arrogant man! You will die of your libidinous thirst for knowledge. Madman, madman! Madman." These lines are heard on the Italian soundtrack, but are entirely silent on the French soundtrack except for the final "Madman."

Or possibly this is a fault only on the Criterion Eclipse DVD edition, but it would seem very unlikely so.