The opera
What opera is being performed in the early scene where Marlene Dietrich's character faints?
shareInteresting question! I don't know.
I suggest you search opera sites about the careers of the two opera singers credited, Gitta Alpar and Anthony Marlowe. Going by Gitta Alpar's career, I've a hunch it may be an extract from the revised version of "Gräfin Dubarry", by Millöcker. That opera was a success for her, and she even played the leading role in Marcel Varnel's The Loves of Madame DuBarry (UK 1935).
Given the deep cultural interests of René Clair, he may have wanted the spectators to link the story he was going to tell us to the centuries old story of La DuBarry...