SALZGITTER, Germany—Late this summer, Nadine Langer took her six-year old to her first day at school. The girl was one of two German children in her class, she said, amid 20, mostly Syrian, refugees.

“I am not against foreigners,” said Ms. Langer, 41. “But there is a point where we have to wonder who is integrating whom.”

Germany’s 2015 refugee...