These mods typically override the local_en.pack with a custom .pack file. Installation is one-click via the Steam Workshop (subscribe, then enable in the game launcher’s “Mod Manager”).
Some mods (like DarthMod Napoleon or Napoleon Total War III ) override the local pack. If you use mods, this manual method might break your mod’s text strings. napoleon total war language settings
If the game refuses to acknowledge your language choice, it is likely written into your Windows Registry. This is common if you bought a retail DVD version years ago or installed a "Gold Edition" that defaulted to a specific region. These mods typically override the local_en