Yeah = yes a) I understand the question, b) it was me, c) i might agree with what you are saying. Nah = No a) I don't think thats right, b) it was not me, c) there is no useful information i can give you, d)come to think of it, maybe i don't agree with you. I dunno = I'd like to put in a disclaimer and nullify anything I just said. Non committal. Common in Australia.