For which there are two systems, one of which stops at ten, and the other is highly irregular in its forms.

I think you mean Wago and Kango counting, in which case Kango isn't irregular at all. There are sound changes, but they almost all follow a handful of basic rules. Wago is plenty irregular, but it also stops at ten and is only used for a handful of things.

And don't get me started on the calendar.

The calendar? Their months are literally just firstmonth, secondmonth, thirdmonth, etc.