The main page of the game present 10 languages translations for each episode, why here on gog this stuff isn't available?
The only official languages for this game are english and spanish, other languages are community-provided, that's likely the reason.
And by the way, while I don't know for the rest, I can say the french translation really feels community-provided, unfortunately. I suppose I should do one myself, but I know for having translated someone's résumé once that a good translation can require a fairly big amount of work...
EDIT : There are two french translations available eventually, my comment was targeting the first and most easily accessible one. I started the second one (from paperyoshis), which is clearly better as far as I checked it.