Fmulder points us to a post on Gamepron, where they reveal that Diablo III has been officially rated MA-15 in Australia, as of September 1, 2011. This is the most restrictive rating, since the R-18 category doesn’t officially exist yet.
This rating is informative, and it’s the first such rating we’ve seen from any area for Diablo III, and the rating is apparently for the full game, not a censored or edited version. A fact the Australians in the comments seem surprised by, as notoriously strict at the Oz ratings system is. You can check the useful chart on Wikipedia to see how Australia’s rating might translate to your homeland.
There’s no word yet on whether or not Diablo III will undergo the same sort of localization process that other major Aussie software releases have required.
[Slightly edited thanks to corrections from the comments.]