I was taught some German by a guy from Cologne.
German tourists asked me “How is Cologne? “ when I spoke.
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!