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?)