Look in the Localization.txt file for what you are wanting to do. That's where the description keys are located for everything as far as I know.
Example:
Took this snippet from the Progression.xml for Attribute - Perception.
attPerceptionRank01LongDesc
Entry in the Localization.txt file for the above:
attPerceptionRank01LongDesc,progression,Attribute,New,"You are pretty oblivious in the perception department. Deal 200% head shot damage and have a 5% chance to dismember with rifles, explosives, and spears.",,,,,