That's sort-of similar (though even weirder than) French[1], where, where you sometimes count in twenties instead of tens. So instead of sixty-nine, seventy, seventy-one, it's (the equivalent of) sixty-nine, sixty-ten, sixty-eleven. And eighty is really four-twenties, so ninety-five is four-twenties-and-fifteen, etc.

Of course, English used to be like this too — thus "three score years and ten". And many languages still retain non-decimalised words for eleven and twelve (and sometimes powers of them, like a gross or mass.)

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[1] Well, French French. Swiss French and Belgian French are much more sensible.