I'd guess in most countries that follow the Name Day[1] tradition (most countries in Europe and Latin America, it appears), Sylvester's day is on Dec 31st[2]. The Germans just use the name to refer to the day (and spell it with an 'i' -- which TIL seems to be the original spelling); dunno, maybe others do too.
At this point I think it's a bit of an NYE tradition on HN to link and upvote that guardian article from 2018. I don't mind it, less confused blank faces when I accidentally recite parts of it to people who aren't German (or Norwegian, apparently)
In general: You should upvote stories you don’t like and be happy. Now you can click on „hide“ and all further submissions will be dupes. Otherwise you‘d see lots of similar submissions of other articles about it.
t. German