I'm not quite sure what you mean? How we create the translation files? Currently we don't need to anymore. That is now a RimWorld-Tool on the main menu, when you have the development mode active (in the options) -> Cleanup Translation Files.
This will create all needed files in your language folder. The files come with the english text as a comment. Not translated texts it is filled there with TODO, so you just need to search for all TODO and replace it with your translation. Works for 90% of the needed files
Just make a backup of your language folder first, in case something went wrong.
Edit:
Sorry, I see you're asking about new string files, that are NOT part of the core data?
Take a look into the file RulePacks_Global: <GlobalUtility.rulePack.rulesFiles> and check out for example the entry AnimalSingularFem
This will create all needed files in your language folder. The files come with the english text as a comment. Not translated texts it is filled there with TODO, so you just need to search for all TODO and replace it with your translation. Works for 90% of the needed files
Just make a backup of your language folder first, in case something went wrong.
Edit:
Sorry, I see you're asking about new string files, that are NOT part of the core data?
Take a look into the file RulePacks_Global: <GlobalUtility.rulePack.rulesFiles> and check out for example the entry AnimalSingularFem