For the Unreal/RTNP/Unreal Gold translation, go here. For the Unreal Tournament 2004 translation, go here. Be aware that some files are shared between translations, most of the time without any difference between them. Files with a shared filename which need a separate translation are placed in separate sections in the same file. (See Engine.int for an example.)
See also Language Guidelines and the language-specifics page for common namings and things to bear in mind when editing this translation.
Between Unreal/RTNP/Unreal Gold, Unreal Tournament and Unreal Tournament 2004
Between Unreal/RTNP and Unreal Tournament
Between Unreal Tournament and Unreal Tournament2004
Other important files
GOTY/Bonus Packs 1-3 Edition additions
Bonus Pack 4