The string eval is an interesting solution, (snip)... unfortunately, it won't be allowed in prod ...

There is nothing wrong with string eval when you have complete control over what's going into it, and there's no real speed issue if it's a 'do once' thing where you use the results many times, and it sounds like that's how you will use it. And it's the only way to dynamically get things into tr/// so you can initialize it from, e.g., a hash, instead of hardcoding the tr/// translations (except as Jenda notes above, by generating the script itself, which is essentially the same thing as an eval anyway).