The Doom 3 Closed Caption (or Doom3[CC]) project team has made the first full release of the closed caption mod for Doom 3 today. To quote the site:
Doom3[CC] is a mod that aims to close caption Doom3 so that hard of hearing and deaf gamers can enjoy Doom3 without missing the important plot details, enemy sound clues and intense atmosphere created audibly. This mod is also helpful for those who wish to learn the English language by reading what the spoken dialog says. This first initial release is an early version and while not 100% complete does provide captions for dialog, monsters and environmental ambience. Future versions will support color coding based on who is speaking and additional languages for the captions.