In the Japanese version, Fox, Falco, and Mewtwo have some additional dialogue for taunts and victory quotes that were removed from the English versions. These lines (and Jigglypuff's Japanese voice) can be heard in NTSC releases by setting the game language to Japanese.
Fox and Falco are voiced by Shinobu Satouchi and Hisao Egawa in battle in all versions of the game. They speak using their English voices only for the Corneria Smash Taunt and for a cutscene in Adventure Mode. Jigglypuff is the only player character who was completely dubbed over.