If extraStrings or the language file work for you on other mods but not the one you want, the issue is likely related to load order.
OXCE can load mods from .zip files and will preferentially load a .zip over an extracted mod folder placed in the same directory. If you're editing a mod directly that is distributed as a .zip file, you need to remove the .zip from your mods folder so your extractef, edited version can load. (Note editing a mod directly like this is not recommended since you'll need to re-apply the edits every time the mod updates)
If you're making a mod of a mod (the recommended method), you should make sure your mod is loaded after the other - use the up/down arrows in the in-game mods menu to put yoyrs lower on the list.