In Germany, practically every town has its dialect. I was told, that in Hannover they speak the best literal German. I have never made it there, so I do not know. Assuming that’s the case, I would advise people learning German in school, to try it there first.
I know in Berlin, I can get around pretty well. But even in Leipzig, I had problems. And further south, it is getting worse and worse.
Asking an older gentleman for Krankenhaus, somewhere in Bavaria, I was given a long, long explanation. The only thing, I understood, was the pointing finger. I drove couple of blocks in that direction and asked again, somebody younger. Ja Bayerisch!
The problem is, that Germans are proud of their hometown dialect. They all know literal German from school, but do not use it. When they realize, that you are not local, they would switch to it, if they realize that the other person is German from somewhere away.
If they realize, that you are English, they often just switch to English. Good for communication, bad for practicing your German.
Unless you plan to learn that peculiar dialect, the trick is to get them to speak literal German, but not English.