When doing an internship in Australia you are able to use the Working Holiday visa. This visa is more known to be used by holiday makers who wish to extend their travel through working, but it also applicable when doing an internship in Australia.
A Working Holiday-visa gives you 12 months of residence and work permit. In Australia you will get the possibility of a 12-month extension if you meet the requirement of having worked a minimum of 3 months within harvest (picking fruit at farms). You can only work 6 months for the same employer. Remember to bring chest x-rays and proof of a health check if you want to work in hospitals, schools or kindergartens.