The look on an American's face when you describe something as being "a fortnight away"

Not sure what that has to do with calendars. Fortnight is just one of many measurements that aren't used a lot in the US (among other places) these days so I wouldn't expect the average person on the street to immediately recognize what it means. There are a ton of imperial measurements that aren't widely used like pecks, bushels, rods, etc.

(I'd also avoid terminology like bi-monthly and semi-monthly as it's a predictable point of confusion.)

Everyone in Britain knows what a fortnight is, and the word is in normal use.

We are confused when TSA staff in the US talk about quart bags.

It’s just not a word in everyday speech.

A quart is the easy one. It’s just a slightly smaller version of a liter. And it’s not like the UK doesn’t use pints which are just half of a slightly larger quart.

I’m sure there’s lots of language including unrelated to measurement which differs across the Anglosphere.

Yeah seeing this today is funny given today begins Rosh Hashanah, the Hebrew new year. But I imagine _most_ countries of the world use the gregorian, especially those on english-speaking sites

Even the 12-hour system (vs 24-) is used by a relatively small minority of Earth's population.

The 12h and 24h system is essentially the same thing, no? In my country we use a 24h system in writing, but mainly a 12h system in speech.

In Punjabi we have divided day into 8 parts, with each 2 parts have names like 1st pair (3am to 9am), 2nd pair 9am to 3pm) third pair 3pm to 9pm & final pair 9pm to 3am.

So, we usually say, 8 o clock in third pair means PM, or 8 o clock in 1st pair means AM.

I think most of the world does that. I don't believe the claims that almost nobody uses the 12h format. At least not without a very thorough survey of the many ways many cultures use time.

In Brazil we'll say things like "The party is at 8 da noite", where "da noite" means "at night". When context is obvious, we often ommit that, so I might say "We will have lunch at 1 one clock" meaning 13h because it is obvious that no one has lunch at 1am. We will generally use 24h time in writing because we cannot control context, and in other situations where ambiguity cannot be avoided otherwise.

To me the main advantage of 24h time is that it is easier to mentally calculate time, so for example 3 hours after 11:00 is just 11+3, which is 14:00h.