I’ve got a good friend who’s Belgain and speaks French and English. I’m going to email her about this :)
The funny thing is that most Belgians I have met (Walloon and Flemish) are at least Bilingual — they speak their native language (French or Flemish) and English. Very few Walloons speak Flemish, and very few Flemish speak French. When communication is necessary between the two “sides,” it is often in English(!).
Another interesting tidbit is that roadsigns can vary as you travel through the country. I work with a group in Liege (pronounced “lee-EHZH”) in the Walloon section. As I leave Brussels, the street signs say “Liege.” Drive a few km down the road, and the street signs say “Liek.” The Flemish name for “Liege” is pronounced “LOOHK” (sort of — the vowel is kind of a “schwa” sound that doesn’t really exist in English) and spelled “Liek.” Anyway, drive a few more km, and you enter Wallonia, where the signs again say “Liege.” Very confusing for outsiders.
However, I can say that the waffles, chocolate, mussels, and frites (invented in Belgium, not France) are good in either section of the country.