There is one book in each of the first 3 acts which teaches part of the Raanaar language when you read it (in the act it is found). If you miss them, or do not read them in the associated act, you will not get the translations. It may be possible to determine what gets changed when these books are read, and figure out a manual way to get the translations....
In any case, you are right that nothing essential is written in ruins, IIRC just pieces of the background story or texts meant to add to the atmosphere, etc. If you skim through the
Beyond Divinity Strategy Guide you should be able to get most of the translated text.