I have a Russian copy of Shield, North American copies of other games, European Mystery Dungeon, and other Japanese games unrelated to Pokemon. The only noticeable differences are cosmetic with the sticker and the cases. They all work the same on the Switch without any issue, and they all play in English.
There hasn’t been any major gameplay variants by region since the early 2000’s, that I’m aware of. All my international copies of games work the same as their counterpart.
I also have Japanese and English copies of nearly every single Pokemon DS and 3DS game, and they all function the same, albeit there’s a region lock on the 3DS family. The switch doesn’t have the region lock.
Tl;dr if you bought an international Switch game, you should be able to play it fully in your preferred language without any issues.
