I can better that as I shared a flat at uni with two guys, one of whom came from Newcastle and the other from Yorkshire.  Two places that are about as close together as they could be (whereas at least there's some distance between Finland and Norway - unless you're far north of course). 

Close as they are, both are rather 'north' for me, but it fell to me as a southerner to translate between the two of them on occasion! 

I never worked out if it was because I spoke a more neutral form of English to act as a bridge, or because I'd spent a year in Nigeria and was more used to "heavy" accents, or because my parents were Geordies originally and I had some vague idea of Tyneside dialect.

On the heavy accents, my Nigerian students were almost incomprehensible to me for a week or three even though they had grammatically correct English.  Then I got my ear in and never looked back (as it were!).  But not before one poor girl had been thoroughly embarrassed because I'd failed to understand her request to ease herself.  Between the accent and the idiom I didn't know for going to the toilet, it was one of those situations that just got so embarrassing on both sides that I just let her go because it must be important if she was so "desperate"!

On the other hand,  I learned things.  Like their use of "so and so pained me" for hurt.  I thought it was just plain wrong but discovered eventually that in very much older English, this was a perfectly correct usage.

 I've often thought more should be made of language differences in Traveller but as was mentioned a few posts ago, its really difficult to manage without it being really tedious.  (Though we did have a lot of fun with sign language in Into the Unknown).  There is, however, an old article in JTAS [GDW] that does a good job of abstracting it somewhat if I recall.  I should make more use of it.

tc