English used to do this too. The most famous example is the first line of Lincoln’s Gettysburg address:
Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.
Joke aside, it's not taught as 4 × 20 +10 but simply “90 is pronounced quatre-vingt-dix” — which kinda is a mouthful, but you rarely count to 90 as a kid anyway.
As guy who hate French language and was learning in 1999 I can confirm it was pain to read the topic of lesson and the date. I was so happy when we switched to 2000.
Whole generations of French students that have no idea they escaped having to write "mille neuf cent quatre-vingt dix-neuf" over and over again, in cursive of course.
Nineteen is dix-neuf though. Which is literally ten-nine. 11-16 all have an equivalent word to the English “teens.” Quatorze for example instead of dix-quatre for 14.
Wait, spanish doesn't do the "we don't have a word for that number, just do math instead" counting system?? I thought the romance languages were tight!
Well, there isn't a word for 99 in Spanish or English, in both languages we say 90+9, so that counts as maths.
If you are asking about words for 70, 80 and 90, that is a peculiarity of French, and not even all dialects, some dialects have septante, huitante/octante and nonante for those.
French is the only Romance language that does the count-by-twenties thing, as far as I know, but apparently some of the Celtic languages do it too. So French may have picked it up from Breton (or Gaulish or who-knows).
The Danish word for 99 is nioghalvfems, which literally means "nine and half five." Which you could be forgiven for assuming meant 11½. The trick is that a) "half five" actually means 4½, as in half less than five, and b) it's implied that you're supposed to multiply the second part by 20. So the proper math is 9 + (-½ + 5) * 20 = 99.