I don't know exactly, but I doubt that in an oral (verbal and direct based) community, accents matter as much as in our Real World (written and indirect based) community.
I mean: many dialects are an obstacle in our world because we don't strive to comprehend our neighbors. We have TV, email, telephone, written papers a lot of other means of different communication which is not dependent on dialects.
In an oral world (like the ancient Earth or Glorantha) I suspect dialects are less an obstacle because people are trained from their childhood to overcome this small but grevious problem. When you have no alternative to contact neighbors except using intermediaries (specialized communicators) or war, you make substantial more efforts before saying "I don't understand your dialect".
> Given that an accent can be enough to make communication
> difficult
> to impossible I would doubt the 'easily'. Once you
> start getting
> dialect words in a conversation it needs a fair amount of
> effort
> to communicate without misunderstandings. The biggest
> problem is
> that many people don't realise that they are using
> dialect words
> because they were brought up with them. A listener from
> another
> area will either mishear the dialect word as another word
> or hear
> a meaningless noise./
(snipped other comments I agree on)