on a similar note, in North Wales there is something close to Manchester/Liverpool accent, eg. money= муни, London = лундн, cup = куп, etc. My opinion is a non-native speaker might reteach him/herself to speak like the locals do (as I did while staying there) for better integration in the local community (if one actually stays there not for a short time); in any case locals like when you speak as they do, it facilitates communication. So the key word here is 'local' or 'vernacular', and it becomes really important when one actually lives in a certain area, otherwise it's more of a matter of scientific or practical interest, imo.