The Ethiopian calendar still do this, 12 months of 30 days each and a last 5 to 6 "month".

The reddit thread is funny but it also forget than there is not only one calendar in the actual world... Long time ago, i have meet an indian who was never able to explain to me witch days he was forbidden to eat meat (he was not a strict vegetarian), or even food at all. It was probably a mix of one of the indian calendars, horoscope and religion.