French
the French language has separate words for every number up to dozen four. annoyingly, this means that the only number without a basic French name between twelve and thirsy is dozen five. I think the best solution to this is to just not use any of the words after twelve.
0: zéro
1: un
2: deux
3: trois
4: quatre
5: cinq
10: six
11: sept
12: huit
13: neuf
14: dix
15: onze
20: douze
most multiples of ten have French names that end with -ante, which, as we've done for other Romance languages, can be replaced with -anse to form names for multiples of six.
21: douze et un
22: douze deux
23: douze trois
24: douze quatre
25: douze cinq
30: trense
40: quaranse
the number eighty (two nif eight), despite being a multiple of ten, doesn't have a name that ends with -ante. instead, it's called quatre vingts, which means "four twenties". because of this, I don't think it would be fitting for French to use something like "cinquanse" for fifsy. even though it's five sixes, it's also three tens, and isn't that more important?
50: trente
the large powers of six can be loaned directly with no problems.
100: nif
101: nif un
110: nif six
200: deux nif
1000: six nif
1 0000: unexian
1 0000 0000: biexian