Depends on accent vs dialect, to an extent. For example, I learnt most of my French in Picardy. The accent is fairly easy to understand, if slightly guttural, but the dialect, particularly when it goes into full-on ch'ti, is pretty impenetrable.

We used to sing Picard songs at school:


I guess a lot of it is how a dead language is preserved in accent and dialect, and to what extent it's used. But it's pretty tricky to understand.

Then, when I studied in Alsace...

Mind you, I used to have a Bourguignonne teacher who was really difficult to understand!