Does anyone know what files for each game should be taken to patch the GOG versions in another language? For example, I have a CD copy of GK3 in Italian and I would like to replace the English audio and possibly the subtitles and the interface as well.
Has anyone tried or has the knowledge to do what I'd like to do with all the games?

UPDATE ABOUT GK3: I've tried to copy all the files contained in the "Data" folder from all three Italian CDs to the "Data" folder of the English GOG version. The game launches and all the written text and videos are in Italian now, but the spoken dialogues skip altogether, ergo, the idea is correct and works but not all files have to be copied over.