Let's face it, the odds of you or anyone else getting a job at DFAT, at least initially, are pretty goddamn low. I realise that everyone and their dog does international relations because they want to be a diplomat, but DFAT's grad program has about 20 places a year and 2000+ people apply to it. So you shouldn't base your decision simply on 'what DFAT wants', because even if you have a few years of Mandarin and have a major in Asian Studies you're going to face a ton of competition. (Unless you happen to be the minister's daughter, in which case they'll give you a job even if you only have third-class honours.)
On the other hand, people with French and qualifications in European studies aren't really going to be in high demand in Australia, simply because Europe is not a particularly important area for Australia strategically. I imagine there would be Australian NGOs wanting French speakers with generic IR or development studies qualifications for work in Africa, but if you really want to work in the European field then actually living in Europe and working for the EU or one of the millions of associated bodies could be your best bet. Typically EU jobs require citizenship of an EU member state and fluency (or at least strong skills) in at least two official EU languages, which for you would be English and French. I have no idea what the competition for EU jobs is like, however.
