Gog says:

Audio and text: English. ? :-) This is not a bug. It's a feature (language is fantasy).

Yes, the characters are using an fantasy language. Most of the dialogue is transported through gestures and mimics though and it works pretty well. Menus are in English (or whatever language you choose at startup). The gamecard mentioning "Audio and Text" is probably just because they had to enter something for Audio, I guess.