Hello and Welcome.
Two Items to consider. Are you interested in translating a specific Marathon Scenario, like the terminals from Marathon Infinity or the Aleph One Interface?
Let's start with Terminals:
Download Atque: http://sourceforge.net/projects/igniferroque/
Follow the manual here: http://sourceforge.net/apps/mediawiki/i ... que_Manual
In essence, you will decompile the map into the various parts. The term.txt files are what you are looking for. Translate those. The folder names are the names of the map files. You may also wish to translate those as well, as the names will show up on the game's mini-map. However, if you do so, make sure the folder naming structure is consistent for the inner files.
When you are finished, drag the file structure back onto Atque to recompile the map. Pass the translated map file around.
As far as translating the Aleph One interface, this can be changed by using mml.
In the docs folder after downloading Aleph One you will find the MML.html help document. The 'stringset' section is what you require. Once the translated strings are in place, the mml can be integrated into a plugin for an easy on-off switch and for distributing.
I do not know of a complete list for stringsets, so hopefully someone else can lead you around there. I can grab STR# values from the old Mac Infinity application, but some will probably be outdated. Let me know, and I'll provide some for testing.