>as Naranja/Uva Academy language classes show, english, spanish, french, italian, japanese and chinese exist in the pokemon world
>the "show a pokedex entry in a different language" feature was mentioned in-universe years ago, meaning german and korean (and american spanish I guess) should exist as well
>there's even the case of XY postgame having Looker not understanding a tourist speaking another language. In western languages the tourist speaks japanese, but in the canon japanese version she speaks english
We know Looker can speak the language of Sinnoh (Pt), Hoenn (ORAS), Unova (BW), Kalos (XY) and Alola (SM/USUM), and yet he can't speak english or "galarian" despite being able to talk to unovans just fine. Moreover, The Hidden Treasure of Area Zero shows Iono, a spanish streamer, is popular in both Spain/Paldea and the US/Unova, and has the language teacher confirming Unova does speak the same language as Paldea.

Therefore we can conclude out of all the regions so far, only Galar speaks "galarian", while Unova speaks "paldean", given Looker has zero knowledge of the english language but he can speak the same tongue as unovans and paldeans. Maybe Alola has the same language as Kanto-Johto-Hoenn-Sinnoh given Hawaii's japanese population, but it's unlikely they would have english if not even Unova does.