I think a lot of it would have to do with the majority over the minority.

Let's take the United States, for example. Say a school were in New Mexcio, they would probably have a large Latino population, and there for would have a lot of food from Mexico or other Spanish-speaking country. Were a school to be in Hawaii or California, with a large Asia population, various kinds Asian cuisines would likely be very popular.

However, Australia doesn't have a very large population as a whole, and would likely have only one school that could accomidate them all. Then we have to look them democraphics of Austalia's population.

The estimated wizarding population (one wizard for 2000 Muggles) would give Australia a population of 11,000. And for Horwarts to have rough student population of 400, we can estimate that Austalia as a nation would have 153 students old enough to attend school.

Now let's look at them demographics for Australian ancestory in this information from CIA World Factbook.
White 92%
Asian 7%
Aboriginal and other 1%

Knowing this, we can expect the school at any time to have:
140 white students
11 Asian students
2 Aboriginal students (or maybe more, please see Wizards and New World Natives )

It doesn't seem like a very high amount, but it could be in terms of my continuing to think in democraphics. I suppose the real question is, would Austalian wizards embrace this small part of their schools population, or would tend to take the more majority-rules thing.

Who would have thought talking about food would be so political?