So what are you suggesting? Should Belgium just ignore their own languages and switch to English because Dutch and French are meaningless in our world?
Actually that's what is done in Bruxelles : it's in the Flemish part of Belgium, the dominant language is French but when they have to communicate with each other, they often switch to English.
No, what I'm suggesting is a little more comprehension from both. Francophone could at least try to learn basics of Dutch (actually a lot try but francophones are not naturally gifted with foreign languages

and Flemish is particularly unpleasant to a francophone ear) and Flemish should stop being rude with everyone who speak French, maybe Walloons would stop teasing them