The west inherits from the Romans, and Julius Caesar standardized away the Roman intercalary month by glomming it into Feburary. Before that a "priest" (the pontifex maximus) (in scare-quotes because it was a political office) would add that month on an ad-hoc basis. Not so different!
It's not odd as in a more unusual system, but odd in that it is widely incompatible with the calendar of most of the world, but still official calendar. Kinda like the Kodak calendar (which was instead 13 28-day months (364 days), and iirc does the off-day adjustments over the corporate winter holiday...actually pretty reasonable)
There are good reasons for the Gregorian calendar’s oddities, though. Any simple system stops being simple when you apply it to enough different situations. I am not sure programmers would like it better if each country had a different calendar for each season. Because a day that starts at 6 and ends at 18 would make sense 2 days each years here in Europe. Not even that if you go far enough North.
https://en.wikipedia.org/wiki/Ethiopian_calendar
The Ethiopian calendar has twelve months, all thirty days long, and five or six epagomenal days, which form a thirteenth month.