[Ingaz]

I think every natural language is irregular when it comes to numbers.

And about Japanese: you forgot about counters for men, animals, flat things and so on.

You have ichi-ippiku-ippon-hitory - issai And absolutely fascinating "system" for "years old" - everything starts with -sai but 20 years is "hatachi"!

[Tor3]

Counters are a different story than numbers. The numbers are highly regular, with the tiny exception that numbers 4 and 7 technically have two variants, where in certain areas one is preferred more than the other, and the pronunciation of 9 when talking about time. But that's really minor.

As soon as you're starting to count it's different.

[boxed]

> I think every natural language is irregular when it comes to numbers.

But.. it's not. Japanese is not. Just because it's not metric with grouping doesn't mean it's irregular.

[samus]

Not being decimal is not the issue. The irregularity are special rules for certain numbers or ranges of numbers for which another pattern has to be used.