Multilingual States :

Switzerland

Belgium

Southern & Northern Belgians - Souther aka. Walloons speak French. Northern aka Fleming speak a dialect of Dutch called Flemish.
Antagonism - aggravated by economic and political differences. Apparently French was off. language.

Key to peace - a very decentralized government in which local authorities hold most of the power and decisions are frequently made by voter referenda.
Languages - German(64%), French(20%), Italian(7%), Romansh(1%).
Off. Language - Romansh in 1938.

Division - Flanders and Wallonia
Difficult - people living near boundary may use the other side’s language.
Example - Voren in Flemish and Fourons in French. Mayor refused to speak Flemish.