Simple reply: Multicultural societies in Central Europe did not disappear simply because people couldn't live together. They were deliberately destroyed, first by a political movement that was unprecedentedly vicious and violent in its hate and in its determination to exterminate Jews - then by traumatised societies lashing out in brutal revenge as a response against Germans whether they were Nazis or not. If you don't create a militarised death machine to exterminate millions of people, then, yes, people with different languages and religions can live together reasonably well.

Most people in the world have met at some time or other a person from a different background, and 99.999999999999% of those encounters did not end up with one person murdering the other. In history, multi-national, multi-cultural, multi-ethnic, multi-lingual states are the norm; nationalism is a very recent invention. (The idea that China is and has always been some kind of mono-ethnic empire is simply ahistorical. Look it up.) Not to mention that many mono-ethnic states have fallen apart or disappeared over the years.

But really, once he starts talking about the tired far-right meme of the Belgian Islamic party, he gives his game away. That party is written about by the far right outside of Belgium one hundred times more than it's been written about in Belgium. There's no Sharia Law in Belgium, and there won't be: it's a a total strašidlo of the loonball extremists who are so wrapped up in fear and hate that it's a wonder they can even breathe without collapsing from fear that a Muslim may have once breathed the same air. Take some advice: get out more. Meet some people. Maybe read a book. Stop spending so much time on websites that tell you to hate and fear your fellow humans.