Corrected entry: Throughout the movie, it is established that the Vikings have an Irish accent, or relative of. All the adults have the accent. Yet Hiccup does not. He is born and raised around them, yet he seems to not have any hint of an Irish accent. He only does once during the film, and that is when he is imitating his father's voice. Other than that, he does not have an accent to match his kin. In fact, none of the teens seem to have the Irish accent, which makes no sense.
Christaffa
25th Mar 2013
Correction: It's a Scottish accent not Irish, and since Vikings would not have been speaking English anyway, the accents are mostly irrelevant.
Christaffa