>>58548934according to npcs in paldea unovans speak the same language as them. Not to mention paldea is both portugal and spain, which is way more than even just the two languages. And what about the protag in alola moving from kanto? I guess he could have learned english before, but what about lillie dropping everything and moving TO kanto? She just gonna learn japanese on the way? Only a couple random NPCs have ever seemed confused by language, and tons of them can speak the languages of any given region fine. Is everyone story relevant just coincidentally a polyglot? Oh and not to mention that they have a completely different script that's the same no matter if you're in poke-japan or elsewhere, unlike IRL.
or maybe gamefreak haven't made up their minds about how they want to handle language. Could be just like earth. Could be a global language. Could be something else. That's the truth: we don't know, it's a stretch to claim anything strongly like that...