Would an average German have been able to go to a restaurant and buy tacos? Would they have a concept of tacos through media? How, if at all popular was Mexican food at the time?
I can tell you that in the northeastern US in the 60s, I didn't even know about tacos. I wouldn't have been able to buy them in my part of NJ even if I had known of their existence. So I'm guessing they were pretty much unknown in Europe.
But for a possibly more authoritative source from the Smithsonian..
http://www.smithsonianmag.com/arts-culture/where-did-the-taco-come-from-81228162/