# Why do the French count so strangely?

Today I’ve heard a talk about division rules. The lecturer stated that base 12 has a lot of division rules and was therefore commonly used in trade.

English and German name their numbers like they count (with 11 and 12 as exception), but not French:

  # |   English |           German | French
-----------------------------------------------
0 |      zero |            null  | zero
1 |       one |            eins  | un
2 |       two |            zwei  | deux
3 |     three |            drei  | trois
4 |      four |            vier  | quatre
5 |      five |            fünf  | cinq
6 |       six |           sechs  | six
7 |     seven |          sieben  | sept
8 |     eight |            acht  | huit
9 |      nine |            neun  | neuf
10 |       ten |            zehn  | dix
11 |    eleven |             elf  | onze
12 |    twelve |           zwölf  | douze
13 | thir|teen |       drei|zehn  | treize
14 | four|teen |       vier|zehn  | quatorze
15 |  fif|teen |       fünf|zehn  | quinze
16 |  six|teen |       sech|zehn  | seize
17 |seven|teen |       sieb|zehn  | dix-sept
18 and 19 are "regular"
20 |    twenty |          zwanzig | vingt
21 |twenty-one |  ein|und|zwanzig | vingt et un
22 |twenty-two | zwei|und|zwanzig | vingt-deux
23 - 69 are "regular"
70 |  seven|ty |         sieb|zig | soixante-dix = 60 + 10
....
80 |   eigh|ty |         acht|zig | quatre-vingts = 4*20 ?!?!
81 |eighty-one |  ein|und|achtzig | quatre-vingt-un = 4*20 + 1
...


So my question is:

Why do French count so strangely after 79?

(Are there other languages that count similar? What’s the historic / mathematical reason for this system?)