Heh. There are a few of us who have motorcycles with US license plates, which are parked in Germany. They’ve been there for an eon. We ride them every year. They are kind of fun in that they’re distinctive - and of course radar traps can’t register them. 
Occasionally we’ll get stopped by someone, but in Germany it’s common enough to see US plates anyway from all the military bases. Of course we have passport stamps indicating that we haven’t been there for years either. No one has ever asked us about how the bikes got there though, I guess it’s just always been assumed they’d leave… eventually…somehow… along with us. That they don’t actually, no one ever thinks much about.
The bugaboo is typically insurance. You can get greencard insurance from a couple specialists but it’s not super common. And while the police are likely willing to overlook a foreign plate, they are likely going to nail you to the wall for not having insurance.