Even before the advent of LLMs, I have personally (and largely successfully) translated several production systems from one language to another. I've learned it

Even before the advent of LLMs, I have personally (and largely successfully) translated several production systems from one language to another. I've learned it's best to start with a mechanical translation, literally bug for bug, leaving shit exactly as I found it (just in another language.) I've done Perl to Java, Java to Kotlin, Python to Ruby, Ruby to Java, C to Swift, you name it. It's only when you change behavior during the rewrite that it becomes an intractable problem. If you ship a 1:1 translation, THEN you can start going through the list of "bugs" you found along the way. Tread carefully when it comes to this, however, as I can almost guarantee that within your non-trivial codebase there will be some code that implicitly _depends_ on a "bug" to function at all. This where shit hits the fan.