I've read a similar question here which mainly dealt with why English only has eleven and twelve as unique words with some interesting ideas. But my question is why do different languages have different cut-off points for unique words. Here I am using unique just to mean words which follow a different pattern to simply number + the word for ten, or which are formed differently to the other numbers between 10 and 20. French for example goes up to 16 before saying 10-7, 10-8 etc. and I just found out that Spanish and Portuguese go up to 15.
Checking online I can see that Catalan and Italian follow French, going up to 16, while German, Dutch and Nordic languages follow English and stop at 12 . Greek also acts similarly and has 11 and 12 with different forms to the other numbers. Gaelic, Romanian and Hungarian have no unique words between 10 and 20. Finnish and Czech appear to also have no unique words (or all unique words depending on your outlook: they use a suffix different to the word ten). No offence to it, but Welsh is a mess. Latin itself has 11-17 following one pattern, and 18 and 19 with a different pattern.
So it seems that in Europe only Germanic and Romance languages have unique words between 10 and 20. Modern Germanic languages all have 11 and 12 as unique words, while modern Romance languages are split between 11-15 (Spanish and Portuguese), 11-16 (French, Catalan and Italian) and none at all (Romanian).
I'm mostly curious as to why the numbers 10-20 seem to have more differences between languages than any other set of numbers (after 0-10 of course). And why these words in Romance languages seem to have splintered due to geography while in Germanic languages they haven't?