Yeah, it also a lot that the person doing the translation is the lead developer of the project who is very familiar with the original version.

I imagine LLMs do help quite a bit for these language translation tasks though. Language translation (both human and programming) is one of the things they seem to be best at.

Agreed, however, I'm quite sure 25,000 lines translated in "multiple months" is very "slow", for a naive translation between languages as similar as C++ and Rust.

2000+ lines/day chunks are 10 days for 20+k lines...