How did Belgian French develop different number words from French spoken in France?

How did Belgian French develop different number words from French spoken in France? Once upon a time, French was not a language, but an entire language family — the “languages of oïl”. Because they had in common their word for “yes”… From “oïl”, pronounced /oh-weel/, came “oui”, prounouced /wee/. (The duration of ‘ee’ is short, though.) A narrow language family it was, yet still: The different ‘dialects’ could hardly understand each other: They differed in their different mixtures of Latin/Roman, Celtic/Gallic, and Germanic. Also: different phonological evolutions didn’t happen the same everywhere. You can see some remnants of that in English. By far the biggest infusion of French words happened in the centuries after the Norman conquest of 1066, when England was ruled by the Anglo-Normans (who brought along their Norman French dialect). So that’s why “excellence” (an old borrowing) is pronounced differently from “par excellence” = /par excellãs/ (adopted much more recently). Sometimes English has even fossilized old/middle French pronunciations, like in lieutenant = /lef-te-nant/[1][2]. Anyway, after the French Revolution (1790s), a very aggressive effort was made to impose what in the map above is called “Francien” onto all oïl speaking areas. And also to the areas within France where “languages of oc” were spoken, such as Provençal. (Those resembled Catalan, where.) Later, after the Belgian independence of 1830, that effort was adopted in Belgium by the ruling classes as well (in Wallonia and Brussels, and Flanders as well for higher education). Children were disallowed from speaking their home language/dialect in school. However, some dialectal words and expressions just stuck around… Because they were just too ingrained, or because the official French version was felt as being too weird or alien. For example, the Celtic habit was of counting per 20 — not 10. Belgium (including Wallonia) was not Celtic. There are hardly any Celtic words in Walloon. So it was plain bizarre for them to all of a sudden call 99 “four-twenty-nineteen” (quatre-vingt-dix-neuf), even for the teachers. So they just kept saying “ninety-nine” (nonante-neuf).