I was involved with a German woman a while back who came from a part of Germany called Hesse. I asked about Palatinian, the language directly to the south spoken in and around Frankfurt in the Rhine River Valley. I asked if she could understand them, and she said,
If they don’t want you to understand them, you won’t understand them!
This shows how speakers of closely related dialects and languages can adjust their speech to become more or less intelligible to each other based on whether they wish to be either understood or not understood.
Many people in Germany say there are no more dialects or sublanguages and that everyone can understand everyone. I beg to disagree. For instance, an informant from a village 10 miles north of Frankfurt said that if he spoke the dialect of his village (technically simply a dialect of the Palatine language Frankfurtisch spoken in Frankfurt) in the city of Frankfurt, he will not be understood! In order to be fully understood, he would either have to speak Frankfurtisch Proper, the language of the city, or Hochdeutsch, the official language of the country.
If even dialects within “dialects of German” 10 miles away from each other can’t understand each other, I really doubt that the dialect situation in Germany is dead and they can all understand each other!