[fauigerzigerk]

That is one weird conclusion. The fact that there are still traces left from past migration waves is hardly evidence of failed integration.

How many generations does the ancestoral language usually survive? Two? Three? Integration succeeds en masse all the time, especially where religion doesn't interfere.

It's just that nationalist wars make more headlines than all the kids I went to school with who didn't even properly speak the language of their own mothers (something I find rather regrettable).