"Wait, that was supposed to be 'Yo soy Groot,' not 'Yo soy Groot' ..." "Get your s**t together, Vin."
Yeah, instead of letting foreign fans figure it out for themselves ("Hold on, is that tree guy still Groot?"), Diesel redubbed his line in a new language for each international version. The dedicated actor learned how to say "I am Groot" in Hungarian, Hindi, Czech, Polish, Spanish, Portuguese, Ukrainian, Mandarin, Japanese, French, Italian, Kazakh, German, Russian, and, you know, English. And he wasn't just mindlessly reading from a prompter, either -- even after the movie was finished, he was still able to remember several of his non-English lines when put on the spot by Jimmy Fallon.
To top it all off, Diesel was so dedicated to his craft he wore stilts during filming (and to the premiere, and on the set of Furious 7, for some reason) to better get in the headspace of his vertically enhanced character.
Going to the bathroom in that thing took some serious aiming skill, though.
Meanwhile, Bradley Cooper (the voice of Rocket Raccoon) didn't even try to fight an alley cat over a half-eaten sandwich he found in a trash container. It's clear who was phoning it in.