an old Weihnachten world that went under

[Coffee Break]

I encountered the expression "an old Weihnachten world that went under", but am struggling to understand it. Could you please let me know what it means? Here is the excerpt:

If I were a better son, I’d do what the father of that dying princess promised he’d do for his daughter each year. I’d bring out his old bones so that he might feel the winter sun again and shiver at the thought of good mulled wines and thick, warm butternut soups sprinkled with diced chestnuts, bring out his body to savor the elegy of moonlit snow as he dreams of an old Weihnachten world that went under and of a love that addled before its time. It didn’t addle, it never happened, he used to say, and for all he knew, the other woman never knew she was the light of his one short, unfinished life—a love most chaste, a love most chaste, Your mother never knew either, and no point telling her now.

- André Aciman, Eight White Nights, Eight Night

This is a novel published in the United States of America in 2010. This novel is narrated by the nameless male protagonist. The protagonist meets Clara at a Christmas party in Manhattan. Now, the protagonist is thinking what he would do for his late father had he been a better son.

In this part, I wonder what the underlined expression means.

I learned in the dictionary that "Weihnachten" means "Christmas" in German, but as for the "went under" part, I have absolutely no clue, unless that is a sunken, underwater world... So I just wanted to ask you.

 

[Tdol]

I think he means that the old Christmases have ceased to be.

 

[probus]

And, as I've previously pointed out, Aciman is not a native speaker of English. His writing contains a lot of weird stuff that native speakers would never use. He is not a writer that learners should emulate.

 

[Coffee Break]

@Tdol and @probus,

Thank you very much for the explanations.
Then it means the old world of Christmas (the past world where Weihnachten--the old form of Christmas perhaps--used to exist) now ceased to exist, by going under the ground, to the underground world governed by Hades perhaps.

I sincerely appreciate your help.

 

[probus]

One final note: "went under" probably has nothing to do with Hades or the underworld. It's probably just a colloquial synonyn for drowned.