I’m not sure, but here’s a guess.
If we look at the original, we see that the judge is referred to as “le premier président de Mortemain,”
Mais Padoie, saisi soudain d’une colère folle, balbutia:
—Où … où … où nous sommes.... Malheureux … misérable … infâme.... Où
nous sommes … Chez monsieur le premier président!… chez monsieur le
premier président de Mortemain … de Mortemain … de … de … de …
Mortemain.... Ah!… ah!… canaille!… canaille!… canaille!…
I can’t find a real town named Mortemain (perhaps this is the judge who deals with the legal matter of mortmain?), but the fact that this was translated to “judge” makes me think that the author is talking about the président of a Parlement, which office Wikipedia assures me only existed up to the Revolution (meaning the story is set before Maupassant was born, but that’s not impossible, I suppose).
Anyway, during the pre-Revolution period, I believe, “mademoiselle” would have referred to a unmarried woman of quality, which is to say an upper-class woman. “Demoiselle,” which is what Varajou says when the translation says he’s looking for “girls,” would just be any unmarried woman, but of course Varajou means to talk about prostitutes.
But he’s talking to a waiter who might not be so smart:
“Tell me, where does one amuse oneself here?”
The man looked stupid, and replied:
“I do not know, sir. Here, I suppose!”
Or might be elderly and potentially hard of hearing:
“Thank you, old man. There is something for you.”
And who, most importantly, probably speaks very good Breton and very poor French:
The peasants did not understand his explanations, the collector did
not understand their line of argument. He spoke French, they spoke
Breton, and the clerk who acted as interpreter appeared not to
understand either.
So when Varajou says “demoiselles,” the waiter hears “mademoiselles.” And in a small, sleepy town…
He sauntered slowly through the quiet Breton town, so sleepy, so calm,
so dead, on the shores of its inland bay that is called “le Morbihan.”
He looked at the little gray houses, the occasional pedestrians, the
empty stores, and he murmured….
…the only young “ladies” are going to be the daughters of the judge!
No wonder the waiter was confused!