If I take a look on Steam, it´s 3€ for europeans!
And you are right, would be nice to have those languages on here!
Could you send a message back to Oddworld about those issues? (Price and languages, or at least languages?)
Here´s the answer and it looks out pretty nice, but wasn´t dealing with the langage issue:
"The simple answer to that is that GOG.com is very restrictive about the prices that can be given to games. There are only a limited number of set price points, and that price point was the one most sensible to us at the time.
GOG.com may have changed its pricing strategy since then, but we haven't looked into it. It may be time for us to do that. Thanks for the prompt!"
Looks like those two games simply have been rerleased here at the time 5.99$ was the lowest possible pricing point!