Ico is a game full of mystery and minimalism, and the story about the boy with the horns and Yorda barely contains any dialogue. At least up until now.
77 unused subtitle cards have been discovered in the game's files which Glitterberri has bothered to translate. Originally the game had 115 of these subtitle cards, but the creator Fumito Ueda chose to cut out 77 of them in order to let the relationship between Ico and Yorda develop without much conversation.
The translation of the discovered subtitle cards does, however, make the story a bit meatier.
Warning: Spoilers!
In the game you encounter an evil queen who claims Yorda is her daughter, but according to the new findings this is not the case. When addressed by the queen, Yorda actually objects:
The queen: "Come along, now, Yorda. "
Yorda: "You are not my mother!"
The queen: "Disobedient child..."
The back story of these two also get richer with the dialogue that was cut from the final game:
The queen: "I have had enough of waiting. Yorda, please try to understand. I do not wish to hurt you You have always been at the forefront of my thoughts, and yet... You say you intend to leave me and run off to who-knows-where? You cannot live outside these walls."
Yorda: "I know that."
The queen: "Then why aren't you here by my side?"
Yorda: "I'm not coming back. You've got it all wrong, Mother. I'm going to live the way I want to. Even if I have to pay for it with my life. It's far better than surviving on the sacrifices of an innocent people."
If you want to read all the dialogue, both cut and uncut, check out this link.