>>40096411>In the movie if Pokemon are only able to understand the general gist of what you're sayingYou don't know that they are that limited, even if they are the answer is the same as the games and anime, Training.
My guess is the language barrier isn't because they pokemon so much as wild pokemon in region/city that bans pokemon battles and capture. There is literally no reason or pressure for wild pokemon to learn human speech or mannerisms if they don't want to unless they want to wander into the city where it'd be useful thing to know to not be booted out as a nusiance. The bulbasaur were isolated way outside the city, they didn't seek out human contact and probably didn't encounter it often, seemed to have no interest in the city so probably never learned how to communicate with people until Tim came across them. Regardless Harry's Pikachu demonstrated repeatedly that the Pokemon do have a complex language of their own so it should be hypothetically possible for them to learn human like Meowth but probably not speak it like him.