The biggest thing that I recall is, and this is arguable as it really depends on who you ask, that Edelgard was a little more overly aggressive and crazy in 3H because Edelgard is not a very PC or pozzed character so the theory is that the translators made her more bad then she was intended. It isn't really a huge deal from what I remember unless you're a massive Edelgard enjoyer or something, and Edelgard is so controversial that unless you really know how to read moon you won't really know how true those statements unless you do the legwork yourself.
Claude's characterization I recall being kind of fucked because he's hinted at being more passive aggressive and pessimistic in JP, someone who talks about a lot of things he wants to believe but can't really bring himself to believe for most the game. He's like a strange take on the whole "We will stand together my friends!" attitude you see a lot with protagonists in war stories, because it is implied that he doesn't really believe in all that but he says it for his own personal ambitions and as a way to peep talk himself. He's the type who feels like he doesn't really have the same solid convictions as the other lords until the end of the story where he is willing to take a big risk to win the day when in the past he might have run away or hesitated, which a nice contrast from Edelgard and Dimitri who are very conviction driven from the start.
In EN he's more upbeat, snarky, and goody goody to be less offensive I guess. Claude's actions don't change or anything, but how he conveys himself is subjectively weaker because it makes his whole "We will stand together my friends!" speeches by the end weaker because in JP he actually believes that now while EN he just always talks like that so it isn't a big deal. Which is unfortunate as Claude is the most boring of the three lords, albeit by far the least offensive, and he desperately needed some spice in 3H.
Dimitri I'm pretty sure is fine, I don't remember any big scandals with him.