http://sourcegaming.info/2016/08/21/pokemon-and-smash-masuda-x-sakurai/

>Sakurai: "I thought it’d be good if we could release Smash in North America and Europe at the same time, but it turned out to be very difficult because of the voices for individual Pokémon."
Masuda: "The voices for Pokémon?"
>Sakurai: "That’s right. Unlike the mainline games, Smash uses the voices from the anime, and in Europe the same Pokémon will have a different voice actor in each country."
Horii: "Is that so?"
>Sakurai: "Since there were so many, I couldn’t fit them all in…"
Masuda: "And you needed to have all the voice actors record their lines…"
>Sakurai: "So I had to wait for all the recordings to come back…"
Masuda: "That’s pretty difficult. But Pikachu, at least, shares the same voice actor across the world."
>Sakurai: "Even in all versions of the anime, it’s Ikue Ōtani, right?"
Masuda: "That’s right. Pikachu is the only Pokémon that’s like that. We did that so the name “Pikachu” would be universal in every region of the world."