... They are very different from each other regarding pronunciation and accentuation, but the vocabulary is almost the same in all German dialects. The difficult thing could be omissions of letters and different stresses of words.
Many dialects have an own grammar, and a large amount of own vocabulary, or other meanings of vocabulary.
For example, in the high German dialect, there exits both Frau (Woman), and Weib (Woman, highly pejorative).
In my home dialect, (itzgründisch), "wife" is not pejorative. There are a lot of misunderstanding, caused by this reason.
A colleague mentioned, that her father in law had called her "Weib" - and she was very upset. I asked her, from where he came, whether it was "South Thuringia wood" (südlicher Thüringer Wald), and she was very astonished, because it was right. I just thought, he did not want to upset her, so I guessed the region.
The grammar may be different and cause different usages of the standard language, too.
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By the way: the standard language is a dialect, only, it is standardized.
A dialect is a language, not just bad language.
Standard German is a kind of saxxony dialect with northern pronunciation.
It was founded in some way by the Bible translation of Martin Luther.
When the low German people learned it, they learned it by using books. So they spoke like they read. In the south, it is other. The standard German is much more different to the local language (if you do not consider low German in the North).
There is a saying, that a linguist once said something like
"A dialect is a language with an armee."
I just wanted to mention, even if you suppose you understand the dialect, maybe you translate wrong. You should everytimes consider the context, and that people usually are friendly.