Thanks for the response!
The INTERRO_DEP's are used to unlock STR_PLASMA_WEAPONS (any one soldier + elerium), while the dependencies for STR_PLASMA_WEAPONS are used only to ensure that it cannot be unlocked by accident.
I have a different mod that I used for debugging purposes, which adds lots of several items at the start of a game (I use it to quickly simulate antire games), which adds STR_ETHEREAL_ENGINEER. I didn't realize that the Ethereals don't have engineers.
Removing the engineers from the debug mod, I am still getting complaints about STR_ALIEN_ALLOY, though the only place that I used it was as an item added to the base inventories at the start of the game. I don't think it is the debug mod causing the problems this time, as it was working previously (without the engineers).
I attatched the DEBUG mod (minus engineers).
EDIT: Removing STR_ALIEN_ALLOY the debug removed [ERROR] Failed to load item STR_ALIEN_ALLOY; but the crash persists.