Yeah, bundle a copy of the module folder of the DLC with your translation on top and click to check the DLC requirement in the Workshop mod profile page so that only people who own it can play it. That should be it. There's no way for the game to know what you are trying to do, each mod works independently. At the very minimum there should be a
module.inifor the game to detect the folder and appear in the drop-down list. So yeah, duplicate everything.