Most MC that get transported in a isekai receive the translation skill, even if they receive a shit skill, super weak or useless before they find something better if they were summoned with magic the translator is there as passive skill.
The few that don't have it had a constitution that refused anything weird installed in them or got to the isekai with another method, this MC case is a combination, he got summoned in this isekai but his body was made with the character he had in game and can't accept that world buff, at the same time this shuld mean that he should be immune to curses or slave magic, I guess it will be a future arc that covers that kind of stuff.
The MC learning the language quick is because most authors dislike making the communication between the hero and everyone else weird, is even hard to portrait correctly, it works for a while but then it gets even on the reader nerves.
some example of no auto TL: Gate, this serie, the manga with the space officer crashing on a planet of sword and magic, most isekai where the MC got reincarnated like a baby and had to learn it like Mushoku Tensei
auto TL: ...most isekai, even some waste a few panels describing how the MC does it, I only remember slave harem having the MC being able to use only 1 language of the foreign world and having to use a slave to trade stuff because it wasn't the most used one, in death march the MC have to use points everytime he discovers a new one, in moonled journey the MC can talk with anything alive, isekai ojisan have it similar, it really depends on the author, in some stories the translator skill is a big plot point.