The original scripts for Trails games in particular use a lot of laughter onomatopoeia. To some extent a lot of Japanese writing/media uses it (onomatopoeia in general fits in very easily to the phonetic nature of Japanese), but Trails uses it more heavily than most media I've seen, and more importantly uses a huge variety for its laughter. When I worked on SC, I tried to represent it as actual laughing sounds with similar variety ("haha!" for a short laugh, "ha-ha-ha!" for those drawn-out, occasionally forced laughs Olivier does, the classic "ehehe" for Tita at times, "hmmhmm!" or "hmm-hmm-hmm" for Schera's very distinct chuckle, et cetera) but that's far from the only way to skin the cat.
There's no "right" answer for how to represent that in writing, especially in the dialogue-box format used by Trails and other RPGs. It comes down to translator/editor preference in the end, and how well it reads will often be in the eye of the beholder.