The French have a word for it

Well no they don’t. My schoolboy French informs me that not only do the French not have a word for 70, 80, or 90, and the names for 90 to 99 compound the problem. Let me back up. Of course, there is a way to express the number 80 in French (“quatre-vingt”), but that is a compound of the single words for “four” and “twenty” respectively. The rot starts with 70, which literally translates as “sixty-ten” (“soixante-dix”), and 90-99 introduces a triple word compound (“quatre-vingt-dix”). Since the upper reaches of the teens encompass compounds themselves (17 in French is “dix-sept”), some numbers between 90 and 99 comprise compounds of 5 separate words, eg. 77 = “quatre-vingt-dix-sept”.  I’m not sure how the French education system is set up, but I’m  assuming that French children would learn the names of the numbers from 1 to 100 before they learnt multiplication, so “quatre-vingt” must be perceived as a single word rather than as “4 (x) 20”.  English has “opaque” words for the early teens (“eleven” and “twelve”), but for the rest fall into a familiar pattern where the original elements of former compounds are recoverable form the modern single term (with minor variations as in “thirteen” and “fifteen”).  French differs here as well by having “translucent” rather than opaque variants in the teens: “onze”, “douze”, “treize”, “quatorze”, “quinze”, “seize”, for 11, 12, 13, 14, 15, and 16 respectively.  I call these translucent  because “dix” + “un” = “onze” is recoverable after a bit of work (well, the “un” part at least), whereas “one” is not recoverable in  “eleven”.  And when English moves into the 20s, it becomes quite regular, with the standard pattern [number] + -ty.  + [hyphen] + number.  The French cognitive load is heavier given the greater number of translucent numbers.  What does it all mean?  Given that children learn their native language at the same rate, iot is clear that while not all languages are created equal, the “hard” learning and the “easy” learning seem to sum about the same in terms of effort.