The usage of the term "Quirk" as a way to refer to the series' superpowers, the equivalent name in Japan is closer to "Individuality", came up from earlier scanlations. It caught on so much that the official Viz release, Funimation dub, and even other scanlators had to follow on it, making the term universal among the Western fandom. The French version went for "Alter", which keeps the meaning, is easy to remember and actually sounds pretty cool.
The Italian translation of the manga keeps "Quirk" as the name, while the anime subs went with "Uniqueness".
When All Might sees the fruits of Midoriya's toil on the beach, in the Japanese version, he says "Ohh my goodness!" in Engrish. This is meant to be a comedic moment, but it doesn't come off as such to an English speaking ear. Thus, to preserve the hilarity, and to avoid Lip Lock, it was localized as him saying, "Holy, stinking... SUPER CRAP!"
Tsuyu's insistence on being referred to on a First-Name Basis may fly over some heads due to how it's more formal in Japan to use Last-Name Basis. In the English dub, she asks that she be called "Tsu" as an Affectionate Nickname. While the dub does have most characters on a Last-Name Basis, the insistence on the use of a nickname also covers how "-chan" is an informal and affectionate honorific, compared to how the most acceptable alternative, "Asui-san," is roughly equivalent to "Miss Asui." In the localization of the manga, however, Tsuyu just asks to be called by her first name.
Midoriya decides on "Deku" as his hero name in the original version because Uraraka tells him that "'Deku' sounds like 'you can do it.'" Because it doesn't sound like that in any language except Japanese, most other languages' version of this conversation change it to Uraraka telling Midoriya that she thinks "Deku" sounds cute.
Similarly, the reason Bakugo calls Izuku "Deku" is changed from being shorthand for "dekunobou" or "good-for-nothing" in the original Japanese, to an implied abbreviation of the longer insult "Defenseless Izuku" in the English dub.
Italian translations went with "'Deku' sounds like the name of someone who engages himself in every thing he does"
Jiro receives a slightly ruder and snarkier side in the dub, fitting her Jerk with a Heart of Gold personality more than in canon. For example, her reactions to Yaoyorozu scolding her for shoving Kaminari into the enemies during the USJ attack are quite different in the sub and English dub.
When everybody in Class 1-A selects their hero names, Aoyama and Ashido go right after each other with the names "I Can Not Stop Twinkling" and "Alien Queen", respectively. In Japanese, both of these were considered to be somewhat cringy instances of Gratuitous English, and the class' silent reaction to both was negative. In English, however, "I Can Not Stop Twinkling" sounds utterly idiotic, while "Alien Queen" actually sounds pretty cool, and so for an English speaking audience, seeing both names treated with an equal amount of disdain from the students wasn’t going to fly. As such, in the English dub, the moment was turned into a joke about Midnight having hilariously inconsistent taste in hero names, and the class' reaction was changed to flabbergasted incredulity that Midnight accepted Aoyama's hero name with some minor alterations, while Ashido's hero name was rejected.
Bakugou's choice for his hero name is "King Explosion Murder" (Bakusatsuou). In Japanese, it's rejected because it sounds way too much like his actual name (while also being a bad pun). The English version instead has his peers reject it for sounding both like a villain's name and completely ridiculous.
When Best Jeanist is giving Bakugo a "The Reason You Suck" Speech about being too aggressive, he uses the metaphor of heroes and villains being "two sides of the same coin". In the English dub, he says that they're "cut from the same cloth", which is the same basic metaphor, but reworded to reflect Best Jeanist's Clothing Combat power.
Class 1-A's Rikido Sato has the Quirk "Sugar Dope", which lets him become stronger by eating sugar. The English translation renames his power "Sugar Rush", which describes the ability much better while also removing the drug reference.
Some of Bakugou's nicknames for other students are changed in the dub. For example, instead of "half and half" he calls Todoroki "IcyHot", after a medicine that's well known in the west.
In the scene where Bakugo pays Kirishima back following the Hideout Raid Arc, he has Kaminari go into dimwit mode to distract everybody. However, due to how it's structured, it looks like Bakugo mugged him. The dub throws in an extra line that makes it clear that the money is from Bakugo's own pocket.
Tengai tries to get Rappa to be more respectful towards their organization. Rappa's response is to splice an expletive into his boss's name. One early fan translation decided to translate this as Overhole.
When Mineta first met Eri, he made an incredibly squicky Jail Bait Wait comment by saying he couldn't wait to meet her in ten years, which many considered to be low even for him. In the dub, it was changed to him noting that Eri will become a looker in ten years, which is slightly less creepy.
In chapter 169 Mina wants to show off her breakdance Dance Battler skills. In the original she calls everyone over by saying to look at her, in the official translation she says "Check-check check-it check-it-out."
All Might makes a lame joke by holding a cotton candy and saying, "Watashi ga kita! Wagashi ga kita!" Watashi ga kita is his catchphrase which means "I am here!", and wagashi is the Japanese word for sweets. The English dub changes it to "Fine and dandy! With cotton candy!"
In a flashback, a young Fuyumi refers to herself in the third person, which is a rather childish way of talking, but not nearly as strange as doing so would be in English. The localization of the manga has her speak in a childish way, such as "I'm worried! Dat's all!"
While the English dub was unable to properly translate Pony's Engrish, the Latin American Spanish dub adapted Pony's speech patterns by casting an American voice actress who is fluent in Spanish and English. The result is that Pony speaks with a noticeable American accent and delivers her lines in English flawlessly, as shown here.
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