Greetings,
Yikes...
Since most (all) of the RTS mods use dialogs, you will also have to modify those.
You are going to need some knowledge of scripting and general OFP file editing if you're going to pull this off: Head over to the editors depot (link at the top of this page), and look for some scripting/ dialog editing tutorials.
You may also want to contact the creator of the RTS 3 mod. I'm sure whoever it is will be able to help you with this.
-Supreme Commander PsyWarrior
-Psychic Productions Studios