Concerning Germany, there are a lot of Grey areas. Until not very long ago many Turks did not take German citizenship because not only was it illegal for Turkrs to have dual nationality (with enough loopholes to drive a truck through), but it was technically legally impossible for a Turk to renounce their nationality (and the Turks stuck to the letter of the law where the Turks were concerned). However what in effect happened was that both sides tweaked their laws, and the Turks basically go and pick up their German passports, give up their Turkish passports, but actually hold onto their Turkish ID cards (and can go get another passport tomorrow if they want one). Whether 100% legal or not from both or either side is one thing, but is in fact what thousands do every year.