I had to look this up. What the fuck? They came up with numbers up to 60 and then just said "eh, fuck it" and made 70 "sixty-ten", 80 "four-twenties" and 90 "four twenties ten".
For any other language? The people who speak it decide.
For specifically French? They decided 90 should be “four times twenty and ten” and thereby forfeited their linguistic rights.
Funny you say that, the French are I believe the only nation to have come up with an institution specifically tasked with regulating the French language : l'Académie Française.
They have been around for almost 400 years, are rife with corruption, have produced a new version of the "official" dictionary every 50 years on average (and it's not even a good one), a single grammar book that was so bad and full of ridiculous mistakes that the linguist community have been laughting at them continuously since then, and of the 40 members (for life) none has been a linguist since 1903. And although their enormous wealth has been subsidised by the taxpayers since its creation, the French governement has waited until 2015 to FINALLY require them to submit their accounting to the State accounting supervisor.
So you are very right, the French have foreited their linguistic rights indeed...
The other way around. We started with base 20 everywhere then simplified some of it.
During medieval times it used to be :
10 Dix (10)
20 Vingt (20)
30 Vingt et dix (20+10)
40 Deux-vingt (2x20)
50 Deux-vingt et dix (2x20+10)
60 Trois-vingt (3x20)
70 Trois-vingt et dix (3x20+10)
80 Quatre-vingt (4x20)
90 Quatre-vingt et dix (4x20+10)
Then they switched to base 10... But only up to 70 for some reasons in France. Belgium and Switzerland (and some parts of France) have gone all the way to 100 by using Septante (70), Octante or Huitante (80) and Nonante (90).
We're not that different with the teens. We effectively say "seven ten", "eight ten", "nine ten". You don't think of nineteen as "nine+ten", it's just its own number. Well, the French take that one step farther.
Maybe it's the anglophone in me, but going 1 - 10 then 11,12 (3+10) - (9+10) then adopting a repeating pattern to infinity is more explainable than going 1-10 then 11-15 then a regular pattern for fifty numbers then getting freaky with that pattern up to 100, then keep that pattern until one thousand, then just repeat that pattern til infinity.