In Chapter 1, just after repairing the claw for the tram, hit your objective finder. Follow the blue line into the hall way where you need to go, then stop as soon as you enter the hallway and look up at the catwalk above your head. Ignore the alien for now. Proceed until you find the first corridor on the right. Walk into it there to see writing in an alien language all over. Look down there to see a message that says in English that reads "Don't listen to their lies, read what they're really saying." Continue reading to find a key that shows the alien language, and below that the corresponding are English letters from A to Z and 1 through 0. Although not everything will be legible, you should be able to decipher enough to understand what is written.
In Chapter 6, after you fight the final creature that spills the gas out, there is a dim flashing sign just before the anti-gravity area. This is a codex for some of the letters and all of the numbers in the alien language.