If a second language is to be learned, then Indonesian would be a good choice, as it is spoken by a country important to, and near, Australia. Indonesian is similar to Malaysian (another country important to Australia) and is the easiest Asian language for English speakers to learn.

But before making learning an Asian language compulsory for Australian students, I suggest some cultural training. Teach students about the customs and culture of countries of our region and how to communicate in international English.

The Australian government's New Colombo Plan is intended to give students exposure to cultures in our region. I have proposed extending this on-line:

Presentation notes: http://www.tomw.net.au/technology/it/international_elearning/

Formal published paper:

Worthington, T. (2014, August). Chinese and Australian students learning to work together online: proposal to expand the New Colombo Plan to the online environment. In Computer Science & Education (ICCSE), 2014 9th International Conference on (pp. 164-168). IEEE.
http://dx.doi.org/10.1109/ICCSE.2014.6926448