interesting, this makes me think of Java that requires an IDE to be usable as a developer.

If you weren't used to regular calendars you wouldn't know that "August 10" means "about the middle of winter" either

August 10 is actually the middle of summer oO

EDIT: you are all lying, if christmas movies have taught me anything it is snowing everywhere in the world in december.

Not in the Southern Hemisphere.

Not if you are living south of Tropic of Cancer.

in the northern hemisphere.

If your locale supports them, then all calendars would contain them. I worked in many EU countries a couple of decades ago and they all had them in their print and work calendars and the software had it as well.

Tooling support is generally required to know what specific dates holidays are on as well, and we manage.

people have been using computers to make sense of the calendar since at least as far back as the Antikythera Mechanism. "you need a computer to figure it out" isn't a valid criticism of a date system, it's a tautology.