in principle I don't think there need to be separate articles for different international followers of a fandom, sections or subpages on the fandom pages would work well enough

I agree with this approach. However, I think it might be interesting also to have separate articles describing how "fandom" in general is practiced in different countries/different languages. So, there could be an [[Australian Fandom]] page in addition to relevant info on Australian fans for a particular fandom. As for how these would be categorized, they might fit under "Fandom by Source Community" or maybe a new subcategory (Fandom by Geography?).