I would like to find someone to help with Wordpress design, ideally located in Australia - is there a way to narrow down your search to local area?
Not really. You could put the keywords Australia and web design in your search, since some people might mention location somewhere in the gig. You can also try searching Google with keywords like those and also add Fiverr and gig. That can help since it may catch Australia in the seller’s profile or in another gig, even one that is not visible.
If you are just looking for someone who writes well in your language, reading descriptions is your best bet. Unfortunately some sellers don’t have their real locations set properly and will choose any English speaking country, but you’ll know pretty easily if you read their descriptions and then actually have an inbox message conversation. (If they can fool you with that, then they must write well enough in the language, at least!)