there some miss understanding about Walloon
It's language is a Romance language based on Latin instead of french, it has been dying out of common use due to growing use of French in Belgium history.
Wallon is part of the same continuum than Picard, that is a french dialect, while distinct from it. (As, any dialect or local speech is distinct from standard form of its language that is by definition, an "artificial" elaboration and evolution.)
but in 1815 they french need a translator to talk with a Walloon!, like example "Good bye" in french "Adieu" in Wallon: "Diè wåde"
Adieu or "Dieu Aide". Considering that part of a greater ensemble of religious expression that evolved in everyday life expression, I don't see the great difference.
If it's about graphical one, graphy difference doesn't make linguistic differences.
Whatever you say "Bonjour" or "Bjr", it's still the same. Graphy itself evolve along different lines from linguistical ones : different administration, different inspirations etc.
On a related note, it is not at all unusual for european french-speakers to not understand at all canadian French or african French. It's indeed very distinct ensembles but so far nobody makes difficulties to aknowledge it's the same language.
Remember that before the appearance of mass-medias and mandatory education, french dialects were often very distinct from each other, sometimes at a great point and todays localisms and regionalisms are but of a shadow of this : people being no longer used to this great differenciation can see in these dialects something totally foreign when it's not (the well known principle of "they don't use the same language in the next village/valley")
also was Wallon culture different from the French
That's also another thing : a same language can be used for different cultures. English is as well used for Americans, British, Indians, Australians, etc. and says nothing about the degree of linguistic separation.
It's territory use to be Spanish then Austrian Habsburg dynasty, then they revolt it and form with Flanders the United States of Belgium.
then came the French and invade this new state
Not really.
1787 : Révolution barbançonne against progressists reforms of Joseph II. It's divided from the beggining into two factions
1789 : Belgians actually attack Austrians. Proclamation of Etats Belgiques Unis, as a separate entity not under austrian soverignity (even nominal)
In the same time, Liege known its own revolution, separately, and don't join EBU.
End of 1790 : Austria takes back southern Netherlands.
1792 : War between Austria and France, that tries to advance in Belgium and fail to.
So, chronologically, we can see that French didn't invade Belgium after EBU were created, but after it was crushed by Austria.
Roughly summarized, the following can be considered : Liege is particularly francophile and seems to have supported unification relativly well; Flanders on multiple ground (by exemple the weakening of its maritime trade) was the most opposed, and the rest was roughly in-between while having a francophile bias.
you understand now wiking, why the wallons were not very delighted, with idea to be part of france in 1815.
In 1815, the population wasn't really more hostile to Empire than the rest of the kingdom (Napoleon wasn't at all popular in its last years of reign, due to conscription, weakening trade, exception regime, etc. Apart for maritime Flanders, it doesn't strike me that Beglians were much hostile to maintaining union with France while not showing great distress not being so, it's true and eventually favouring union with Netherlands as a good compromise to avoid being returned to a really repressive austrian rule.
Point being, eventually : linguistical differences being not that relevant, what mattered was the degree of political realism among Belgian bourgeoisie and urban population (the most probably francophile), the reject of imperial regime amongst peasantry and maritime population (as it existed as well in France proper), and of course the allies intention (see above post).
Even if the latter wouldn't have mattered, the two others would have likely played in the maintained division between Belgium and France (at the exception, *maybe*, of Liège) in the form of either a badly functioning EBU (under allied influence, probably British and Prussian, in a first time), or to an unification with Netherlands as OTL (being seen as a compromise in face of austrian or allied influence on Belgium).