With all the characters in this great series, there are few examples of any ethnic characters. Marshal, Lenora, Dahlia, Iris, Erika, Koga, and Brock come to mind. Additionally, you have the Breakdancer Trainer Class, and Ash Ketchum certainly seems to be tanner than most characters in the franchise, indicating he may have Hispanic/Greek/Asian/whatever roots on his father’s side.
But this is a franchise of hundreds of characters we’re talking about - anime background characters, game characters, trainer classes, characters from various manga.
The Pokémon world seems to have very little evidence of any war or conflict. Surge was previously in the military, and there was a war fought in medieval times (as seen in Movie 8). But nothing more than that has really been seen.
The world seems to be very peaceful, and also very technologically advanced. No poverty is seen, either, and religion seems to be a non-existant concept.
What I’m getting at is that, without any of these things, there’s no reason to emigrate. There’s no war forcing you out, no horrible leaders, no poverty, no weird customs - no reason to leave your country.
The people who do move are simply moving to the region X because they want to, and thus they’re a very minor percentage.
One will be family trees, one of which I just posted. The other will be basically random ramblings, which are either too short to put into a headcanon but still worth mentioning, or are headcanons about things other than characters.