I want to add my own mission briefing to a single player map, so I followed the above steps but it didn't work.
I opened assets0.pk3 and extracted briefings.str.
I added my map name (map1) to "REFERENCE", added the new briefing description to "LANG_ENGLISH" and saved the briefings.str file.
I put the saved briefings.str file in a new "strings/English" folder located in Star Wars Jedi Knight>Jedi Academy>GameData>base.
I started the map, but the new briefing didn't appear.
I tried saving the map with the associated files as a .pk3 file too, but the briefing still did not show.
Have I missed something?