Fish Compatibilty

Hmmmm. "In aquaria, Asian barbs have their own way of interacting with shoals of different fish. But the chances are that a shoal of Amazonian tetra won't understand the rules – they've evolved their own ways of fitting in. In some cases, an aquarium is little more than a huge cultural time bomb, waiting to blow." 

I found this way back a couple of years ago when I was investigating options: http://aquariuminfo.org/compatibility.html It looks as though there are a few similar types of ones around although I haven't looked at them in depth.

Helping develop international relations 

That's fortunate, and also interesting.

Originally, I had x-ray tetras and intended to have panda cories but ended up with pygmy cories, so both species were from South America. The tetras didn't exactly treat the cories with "respect" - the males swam so low in the tank and had so many sparring episodes that they knocked over the cories with immense regularity, while the females swam rather intimidatingly immediately behind the cories as they were foraging, in order to get extra food that they unearthed (ie let the cories do the hard foraging work and benefited from that).

I opted for harlequin rasboras (from Asia) due to the similar nature to tetras, albeit from different parts of the world. In the few months' overlap between the harlequins' arrival and the cories' departure , I observed that the harlequins would have made much better tankmates for the cories as they swam higher in the tank and so didn't bowl them over or intimidate them. The two smallest harlequins even seemed to befriend the cories, possibly due to being more similar in size.

I find the harlequins and the x-ray tetras a better "fit" than the x-ray tetras were with the cories despite the differences in geographical origin. The tetras spend most of the morning with the males sparring and then chasing the females, while the harlequins tend to be dotted around the tank, quite calmly but ignoring them. However, in the afternoons, they intermingle more, often by size - the two smallest male tetras sometimes swimming/playing with the two smallest harlequins, or the 4 similar-sized harlequins together, or often one harlequin will take possession of one half of the tank while the remaining 10 tankmates intermingle in the other half. At night, as soon as the light is switched off, they do form species-specific shoals - the harlequins develop an immediate formation in the upper half of the tank, while the tetras develop a looser formation underneath with some jiggling around to identify a suitable spot within that formation.

In my own case, so far, I think size and temperament of fish probably has a greater bearing than geographical origin.