What kind of international law? If you're thinking human rights law - that is a tiiiiiiiiiiny niche and most people won't get to do it - you need years of experience and potentially a graduate degree, at which point your undergraduate uni really won't matter that much. I believe places like the Castan Centre do have programs where they send graduate students to intern at the UN etc. but these are people who not only have amazing marks, but also do things like set up human rights organisations in their spare time lol. So yeah highly competitive and your uni probably matters a bit there.
Most international law is stuff like international trade law, international maritime law etc. which is about as interesting as it sounds. (And also a very niche area. I wouldn't have a clue how to get into that industry even if I wanted to lol.)
Diplomacy - actually I keep track of DFAT ambassador announcements at work, and very rarely do they have law degrees - most are either economics, foreign language or international relations graduates (with decades of experience on top of that). You don't necessarily need a law degree - I believe the DFAT graduate program takes any discipline - so I can't imagine your alma mater would have as much of an impact, as long as you maintain good grades / experience. I have also heard that government graduate jobs, in general, place less emphasis on your marks/uni and more on just how well-rounded you are / your personality/work ethic etc.
Practice - just in general, the market is extremely saturated right now where even Group of 8 graduates with HD averages are struggling to find clerkships/graduate jobs. If commercial law (big top tier law firms) your objective, then maybe a JD at a Group of 8 would be a better idea than ACU.
Deakin is borderline - their law school is really not that bad from what I've heard. I volunteer with one Deakin student and used to work with another (who is now doing a PhD in law) and they are both very competent people. If you can maintain a very good GPA and combine it with things like mooting competitions, internships and other legal experience, and volunteering, you shouldn't be that disadvantaged especially if you go for smaller firms (which coincidentally also have muuuuch better work-life balance!)