@clem @lizzard @sarahbecan Yep, the subtraction thing is fun in Danish and really does your head in.

On the bright side, you can cram these as pieces of vocabulary, and the rest is then just 10-based math.

For Gaelic, they actually dug out a medieval numbering system that is 10-based to teach math in schools. This has the additional advantage of not having to change word order from 39 to 40: In the traditional system, 23 = three over thwenty, 63 = three twenty 'n' a-three.