Alright, I got it.
My original issue was that in SomaDev.bat mode it wouldn't load my english.lang file, but in ModLauncher mode it wouldn't load the original english.lang file. As I found out, the parts of the terminal for FROM, DATE, SUBJECT, SENT, etc. are held in the game's original english.lang, meaning if you want to use them in a mod you have to find them and transfer them over into your mod's english.lang.
This, however, only solved the problem of having the ModLauncher version having missing text, my SomaDev.bat version still wouldn't load my mod's english.lang. After fiddling around in .cfgs, .bats, and a bunch of other files I found out how to make it all work, how to make your mod's english.lang show up in SomaDev.bat (also, how to make SomaDev.bat actually load the level you want and not pitch black).
So here it is: triadtimes' how to set up a dev environment 101.
(This is assuming you are creating a mod in a folder along the lines of redist/mods/mymod/)
After running SomaDev.bat the first time please sit still. DO NOT (as the wiki suggests) CHANGE YOUR dev_user_settings.cfg. Well, you can, just not the change start map part.
Now that SomaDev.bat has run once, check redist/config/ for a file called main_int_dev.cfg. This is the file that will help you out, this is where you should change the map start location (very bottom), an example will look like:
Now, to make your .lang file actually useful! At this point it looks like you can do one of two things 1) find resources.cfg in the redist/ folder and add the line
<Directory Path="/mods" AddSubDirs="true" />
and then save. Or, 2) you can change the line in main_int_dev.cfg that points to a resource file to point to your resource file in your mod, just make sure the one in your mod also has the directory path "/mods" in it.
That's pretty much it!
The issue was that resources.cfg did not have a directory for the "mods" folder.
Of course this is only the dev environment, when it comes time to test/ship your mod make sure your mod's own main_int.cfg and resources.cfg are set up correctly.