Board Thread:Questions and Answers/@comment-26369387-20170812201110/@comment-34801883-20170928051936

the first scanlation group to pick up the series (fallen angels) initially translated it as individuality, as that was a literal translation, but later decided to trasnlated it as "quirk" because it was shorter and sounded better in english, it was a localization decision. it carries that same connatation and is easier to say, so it was a good decision imo. later when the series became more popular and mangastream picked it up, they initially used individuality as well, but changed it to quirk when people complained. when viz started publishing it in english through the english shonen jump chapters (they started at chapter 29~) they also used the term quirk. it's not known if they used this term because it was popular in the fandom and they wanted to attract the fanbase to their translations, or if they saw it and thought it was good and used it, or if their translators came to this decision independently. it's not exactly an obscure word, so I'd buy into it being a coincidence. unfortunately it's not something we're ever going to get confirmation on.

I'm told the spanish translation used the spanish word for individuality, but changed it to quirk in later releases because it's more popular. I also read that viz translated it as individuality and than changed it to quirk later, however I read the initial viz translations and while I no longer have them as I deleted them when I downloaded the volume releases, and can confirm that this is not true. they've been uses the term "quirk" since they started. but I could be full of shit since I have no proof, so who knows.

anyway, viz used the popular fandom term for their official translation, so now it's canon, there's a ton of speculation if it was because of the fandom but I doubt it's true since viz has been perfectly comfortable tossing fan translations that are more accurate/popular when localizing manga in the past, so it's probably a coincidence? on the other hand, quirk is an excellent localization so maybe they wanted it but didn't want to credit people for it who basically steal the scans and release them online ¯\_(ツ)_/¯