I can say this because there is a definite schism between the two characters. Hikari was always soft spoken and hardly never had a mean word about anybody; she was even sympathetic of those who either were fully intending to kill her or use her for bad purposes. Kari, on the other hand, will laugh behind others' backs without a second thought and can be really careless with things she says about people. It's a pretty amazing difference, and it's completely the fault of the localizers that they changed her personality like that. In fact, they kind of ruined everybody in the first three seasons, though more the first two than the third.
They kind of did the same thing for all of the characters in Adventure/02, which sucks because most fan fiction writers have only watched the localized version and have no idea about how the characters were originally written. They also don't know about the fact that most of the names were changed, and a lot of Digimon names were censored, some even in really stupid ways.
Ahhh, I could go on about this stuff all night. I've gone over this sort of thing countless times in the past and going over it again won't change things any. Go find my others posts for more info on my viewpoint of Daisuke/Hikari/Takeru and other assorted things.