> Better yet require YYYY-MM-DD
This is the equivalent of requiring all your text to be in Esperanto because dealing with separate languages is a pain.
"Normal" people never use YYYY-MM-DD format. The real world has actual complexity, tough, and the reason you see so many bugs and problems around localization is not that there aren't good APIs to deal with it, it's that it's often an after thought, doesn't always provide economic payoff, and any individual developer is usually focused on making sure it "looks good" I'm whatever locale they're familiar with.
It's normal in Asia.
I'm not in Asia though.
It's also normal to speak Chinese in China. That doesn't mean that I should be speaking Chinese as well.
> "Normal" people never use YYYY-MM-DD format.
My point was that this isn't true.
And Sweden. And probably lots of other countries too. It's a world standard, and there are very few places that use hyphens in dates that are not ISO dates.