The same was going on in Holland with Indonesians.
I was there too for all of 1975 and twice a year for another 20 years. The Gast Arbeiter were brought in as you say mainly from Turkey. They were supposed to be only temporary but many stayed. Got to know some and left a bunch of household stuff with a Turkish family when I moved back. Those with families seemed to be reasonably normal, but their women seemed to be afraid of any outside the family contact. Single Turkish men were not common then.