There are a few size conversion charts available online that might be helpful (this one is specifically for swimsuits: http://www.theswimshop.com.au/container_size_charts.html - according to that, an EU 44 is an AU 16, but it only goes up to EU 52 / AU 24 so may not be the right guide )
I think your best bet would be to take full measurments and compare them to standard/average Australian size measurements (and put the measurements in the listing, so that people can double-check).
