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It's not a simple question but this part is quite easily found on wiki:
Dutch speaking : 32 + 1,3,5,9 (and 89)
French speaking : 32 + 4,6,7,8 (without 89)
German speaking :? (it's only a few thousand people)
Brussels : 32 +2 has Dutch subregions and French subregions, but those are not seperated with individual phone numbers.
It's tricky to decide for French or English. Because Dutch speaking people in Brussels also speak French, but prefer Dutch or English. French locals need a French service because they don't speak English very well. Still, everyday's language in Brussels is at least 2/3 french and 1/3 Dutch.