Oddly, I believe French as spoken in Belgium actually _does_ have a proper word for 80.

Sextante, octante/huitante and nonante are used for 70, 80, 90 in various French-speaking countries/regions (Suisse, Belgium, parts of Canada (https://en.wikipedia.org/wiki/Acadian_French#Numerals)

I forgot about that one and also the English numbers less than twenty. But in any case, if you consider bigger numbers, the most significant units invariably come first.

Yes, because by the time that the bigger numbers were in common usage, the world had settled upon "big endian" reading of numbers. But it's hard to kill an already entrenched system, thus vier-tausend-neun-hundert-acht-und-dreißig (four-thousand-nine-hundred-eight-and-thirty)

It's not mere convention. Reading the most significant digits first lets you abbreviate in an ad-hoc fashion and it also supports adding more precision as the number is being written. "Most significant digit" is a clue that those are the figures people consider most important in general. They want to hear those digits first, abbreviate or round to those higher place values, etc. So, big-endian makes a lot of sense for writing and speaking. Little-endian really offers no advantages for speaking or writing. And in doing arithmetic, decimal answers expand in either direction (multiplication to the more significant, division and roots to the less significant), so you can't say one form is universally preferable there either. So big-endian wins!

If I remember correctly, I believe French’s vigesimal system is a vestige from the non-Romance language spoken in France before Latin was introduced there. French isn’t the only language with vigesimal elements; English has the word “score,” made most famous by Abraham Lincoln’s Gettysburg Address (“four score and seven years ago…”).

English also has fourscore (four twenty) = 80.