Should be pretty easy, in fact. All of the in-game text is stored externally in JSON and tsv files and read-in at runtime. You should be able to find them in the zip file in the "Languages" subdirectory, if you want to have a look at what's in there.
As for the actual process of making a new language package (and subsequently testing to make sure it works), that's probably a bit too complicated to explain in an Itch comment, so shoot me an email at developer@realitylayerzero.com if you're still interested and I'll walk you through how to do it.