SF characters default to Japanese because those are their “original” voices. They used to have some English-speaking characters in Street Fighter III, but otherwise Japanese is always the default. Tekken character defaults are generally based on what they speak in Tekken, though other languages like Korean or French were not included.
A hot-blooded soldier like Guile shouts Japanese “Sonic Boom” like he’s falling asleep or something. I don’t remember him shouting the move that way in SF IV. D:
Lars’ english voice is actually really nice. I would use his taunt all day, if I couldn’t catch anyone on the wrong foot with it. “Are you prepared to die?”
English all the way. Dat Juri voice…is so CRAAZZZZZZZZYYYYYYY!!! anyway I find english better overall. Suits the characters more. But it’s really all personal preference really.