To add to the discussion, 'dialect' is comparable to 'language' more than accent. As was said, accent is merely the sounds.
A 'language' is a communication system which is idiosyncratic to a group of people, and which can only be understood by those people. So, a person who knows the English language cannot communicate using language to a person who knows the Shona language.
A 'dialect' is a communication system which is also idiosyncratic to a group of people. It differs from language in that other members of other groups can understand each other's 'dialect', but again someone who doesn't know the language cannot know the dialects of a language either.
Sorry, I am reading Fromkin and I refer to her book; "it is not always easy to understand whether "the systematic differences" between two speech communities reflect two dialects or two languages.. when dialects become mutually unintelligible- when the speakers of one dialect group can no longer understand the speaker of another dialect group- these dialects become different "languages".
The boundary between language and dialect isn't always clear. 'Scots' for example, is debated whether it is a seperate language. Even those close to those who speak Scots (i.e English people) have difficulty understanding it. I believe some films that use Scots dialogue have subtitles when shown in England. It isn't just about understanding of course, but also etymology and how the language has developed. A lot of Scots comes not only from English, but also the Gaelic language and from Scandanavia as a result of the Vikings - the Scots word 'bairn' meaning child, for example, when the word in Norwegian/Icelandic/Swedish is 'barn'.
Another example of an unclear boundary is between Norwegian and Swedish. As far as I'm aware, these languages are really dialects of each other, and the distinction to make them seperate languages is a political one rather than a linguistic one. Perhaps someone can clarify, but is there mutual understanding between a Norwegian person and a Swedish person. similar to what would be expected between a person from Wales and a person from New Zealand, for example? Actually, Are you going to mention that the same/similar "dialects" may produce near distance among different languages?
Some dialects are more like the language they stem from, others are closer to being a completely different language. Indeed, there is no doubt that new languages form from initially being a dialect of a language and developing seprately.
