Stephen Sondheim saw Ettore Scola's Passione d'amore in 1983, and this provided his inspiration for Passion. The Italian film, released in 1981, starred Bernard Giraudeau as Captain Giorgio Bacchetti, Valeria D'Obici as Fosca and Laura Antonelli as Clara. It was re-released in the U.S. in 1994, with subtitles, after the opening of Passion. I haven't seen the film myself yet, so I can't offer any personal thoughts, but you can find out more about it at the Internet Movie Database!