That is a modern synonym, but not quite the same. This is more specific for organized indexboxes.
> "(Lern-)Kartei" oder "Vokabelbox".
Those are not even the same. They are special purpose-tools with specific meaning which just happen to use index-cards and boxes in their analog version. That's like saying notebook is not a word because diary is widely used.
You’re defending the claim that Zettelkasten is a commonly used word. You do that by smugly telling GP they need to go to Wikipedia to educate themselves about it. I guess that nicely proves their point?
He is correct though, just because the GP has not heard of it doesn't mean it isn't commonly used.
I'm also a German native speaker and I agree the term Zettelkasten is more common than Karteikasten. I encountered Zettelkasten when I was in high-school a long time ago. That said the way I've encountered it was always more as a study tool (like flashcards, or the vokabelkarten/box the GP mentioned ) not so much for note taking, but then that's what you do in high-school.
I’m also native (NRW), never heard of Zettelkasten before here, we just say Karteikarten (not even -kasten). Same for a Bavarian friend of mine. Where are you from?
No, because nobody can know everything. Even common knowledge is not so common that everyone knows all and the same. And the mention of wikipedia was more to show the usage and origin of this, not how common or uncommon it is. Because that's not really mentioned there.
There is a certain point where few enough people know something that it can’t be called common. Maybe GP is not the exception for not knowing but you are for knowing?
Despite the fact that the https://en.wikipedia.org/wiki/Leitner_system was pushed by just about every teacher.
The usual word is "Karteikasten", "(Lern-)Kartei" oder "Vokabelbox".