OP here. I read a lot of Wuxia novels, some of them are well translated, and I usually end up giving up on the poorly translated ones.

I tried a few models (Gemini-2.5, Gemini-3.0-pro, Claude Opus 4.5), and found that they all improved the quality quite noticeably, even without being provided the source. The trick was mostly asking them to be super conservative in the changes they made.

Here's a diff if you're curious: https://www.diffchecker.com/DKgmzLdM/