Since your German I'd urge you to read the book Strange Death of Europe. Assimilation isn't an easy process and mass migration in this scale is indeed a new thing.
It isn't really and most certainly not for central Europe or Germany. People too often ignore that the 20th century has seen constant and massive population movements [0].
In Germany particularly with Turkish guest workers [1], fall of the Iron Curtain triggering mass migration from eastern Europe, later refugees from the Yugoslav wars mixed in. More migration after the 2004 enlargement of the EU eastwards.
Now you could argue "All these people have the same culture, they are not weird Muslims", which is a moot point because these same "their culture is too different" claims were made about eastern Europeans for many many years before they became part of the club themselves.
It should also be noted that nobody ever talks about the reasons why these refugee streams exist in the first place: US foreign policy.
Even back in 2002 Afghani people made their way to Germany, followed by Iraqis and people from many other MENA countries, fully escalating with Syria.
This isn't some sudden new thing, one could literally watch this happening over a timespan of nearly 2 decades, yet nothing was done. It's so painfully obvious that some people consider this as part of US strategy [2].
[0] http://www.bbc.co.uk/history/worldwars/wwtwo/refugees_01.sht...
[1] https://www.dw.com/en/turkish-guest-workers-transformed-germ...