You can trick the game into doing this, I think. Text is included for all languages in the shipped version of the game; when you tell the launcher to change languages, it just starts downloading the audio stuff for the new language (I think).

I play in English, but within the game I can switch to German (say), and see the text in German, but the audio is still in English. Because I haven't downloaded the German audio.

Does this point you in a helpful direction?

managed to pull it off, essentially the opposite of what you did. i wanted text in eng, and audio in the other language. I downloaded the language changer addon and set the hotkeys, then renamed the eng voice folder after dling the audio language i wanted