That's... actually a kind of big translation difference. [2.5 spoilers]

[axemtitanium]

It was an authorial decision to make Midgardsormr's relationship with the player more ambiguous in the English version, perhaps to set up a more dramatic reveal later. The EN team is no less a part of the lore/story team than any other language, including Japanese. The story in this game is a collaborative effort and the EN team decided to characterize EN Midgardsormr in this way, making him more mysterious, terse, and ambiguously adversarial than his JP characterization. You are free to dislike that authorial choice, but it's no less "correct" than the Japanese version because all people involved are full-fledged "authors" of the work.

[Dyvid]

It was an authorial decision to make Midgardsormr's relationship with the player more ambiguous in the English version, perhaps to set up a more dramatic reveal later. The EN team is no less a part of the lore/story team than any other language, including Japanese. The story in this game is a collaborative effort and the EN team decided to characterize EN Midgardsormr in this way, making him more mysterious, terse, and ambiguously adversarial than his JP characterization. You are free to dislike that authorial choice, but it's no less "correct" than the Japanese version because all people involved are full-fledged "authors" of the work.

Pretty much this. The EN and JP lore master work side by side so it's not the simple read, translate, paste. Its a direct decision to change the wording to make it more appealing to the audience and the general tone of the context is true in both versions. The motivation the same in both version, to test the player in the upcoming conflict.