So you have finished the translation for episode 3 already?
Normally you contact the author, then the author will make a translation file and send it to you,
in this file you write your translation, when finished you send it back and the author compiles it and produce a english.tra file for instance,
which could be used in the game.
I think there is a possibility for "hack" the original game somehow without the sources to produce the *.tra file, but i have no idea how it works and i won't recommend it.
@Kinkilla:
hmm, the chronology isn't that much important (at least not for translating) cause most of episodes are standing for itself and have no connection to other episodes (of course there are execptions).
But for the popularity it would be great to translate first the newest ones, then the most popular ones, before translating everything else.
I don't know if a remake from an existing episode without asking the real author is "allowed",
maybe you could start a community poll and see what other authors think about it.