The files you need to change will be in lang/en. It is normal to have an en folder under lang, instead of a us folder. I don't think you have anything missing.
Be patient, not everyone is online at the moment. Wait at least 24-48 hours to give people chance to help you. BTW Use the edit button, don't double psot
Can you post your DXDiag please. (See here if you don't know how to do that) Have you tried lowering the game display settings in the ingame option menu? Have you tried updating your graphics card drivers?