How do you find the code in a compiled program that’s necessary to make a language patch?

I've been looking into doing this for a few programs I use but can't find any resources about how to do this online. I've tried using dotPeek to find where the UI info is stored, but I don't think that's the best thing to use cus I can't find anything. It also only works for 1 of the 2 programs. I've tried looking for other decompiles, but the sites they're on are either fishy, or are blocked on my college's wifi. So I'm stuck. Any and all help is appreciated.