Issues with accents and humour
I was reading the reviews here and was surprised to find so much vexation regarding the accents in this film. They're pretty spot-on. I've been all over Australia, and plenty of people in Tassie do indeed speak just like Shaz. Lots of people have a more "received pronunciation" as in the character of Doris. There are variations in the Australian accent, not just regional but sort of "class" based as well (for lack of a better term). For instance, I speak differently to some people who hail from the same area as I do.
I think the issue here is that most people just plain aren't used to hearing it in the movies. And a lot of Australians, such as people who live in Melbourne, can be rather pretentious and don't want to risk giving the impression of having no sophistication, etc etc.
It was filmed around my local area in northern NSW, and part of the reason this film appealed to me so much was that it encapsulated so many aspects of the place perfectly. I think a fair bit of the humour might be lost on a foreign audience - for instance, the character of Trevor Blundell being a pisstake on Vic Hislop, the shark hunter, and the broadly accented Shaz triumphing over the wannabe-posh, well spoken, clean cut Australian middle class who often suffer from a lot of cultural cringe and look down on those who aren't so well spoken. Not to mention the unashamedly stereotypical character of "Trout" with the bleached hair, the job at the water park, the silly nickname, the love of surfing, etc - perfect pisstake on the denizens of the Gold Coast (the non-meth dealing ones, at least).
People unfamiliar with the region, such as foreigners and people from Melbourne, would be unfamiliar with these stereotypes, and might not see the humour in the way these characters were constructed. And I guess that is a criticism of the film, that the humour is a bit too localised.