Story is the same. Have you played Tech Demo?
Yeah, Tech Demo is a full game, even that it says Tech
Demo.
It comes from words: Technology Demonstration, which makes it to be very short.
Frictional Games take on into some sort of competition to show what they've made, and that was Penumbra Tech Demo.
Anyway, they didn't win... But they started to share the game for free in internet and that made Penumbra
so popular, that they decided to make it to be commercial trilogy.
However, there were some problems with the publisher (I think it was the publisher...) and they had to cut down the trilogy only into two games: Overture and Black Plague.
Some months after release of Black Plague, news started to spread over the internet that Frictional Games are working on an expansion for Black Plague.
So, to us fans, it was like an trilogy!
Oh, and about your question for the translations: I'll have to say that I have no idea about it, sorry!