gc, you're right about the comma, but the thousands separator is a space, not a dot: 12 345 678,90.
It becomes tricky for the 70s, 80s and 90s because you're under the impression you're doing math by enunciating them, like 90, which is "quatre-vingt-dix" -> (4x20)+10
. In Belgian French, those are just septante, octante and nonante instead of "soixante-dix", "quatre-vingt" and "quatre-vingt-dix"