The show Trawlermen which was shown in the UK was subtitled for native audiences since the accents on some of the men were so thick & unintelligible (at least to my friends' & my own ears in S England).

https://en.wikipedia.org/wiki/Trawlermen_(TV_series)

Edit: Further article on the subtitling and the reactions to it: http://news.bbc.co.uk/1/hi/5244738.stm

The first time I came to the UK, I remember sitting across from some rather loud Scots on the tube. I think they were talking about work; I wasn't sure, because the only word I could clearly understand was "fookin'" (an adjective which can apparently mean almost anything). Definitely not mutually intelligible to my California-trained ears.

There are always people with varying degrees of dialect usage. This fellow[0] is quite, but not totally unintelligible to my English-as-a-second-language ears and there are Scottish where you recognize their origin in the first sentence but still understand them 100%.

Same with Bavaria, really. Most of us from Munich have a very light dialect that's really not that difficult compared to many people from the countryside.

[0]: https://www.youtube.com/watch?v=QrLjsCCGnuo

edit: The Bavarian dialect also has quite a few grammatical quirks, whereas the Saxons just pronounce German very different, but the grammar is very standard.