There's the one modding API and that's about it. Hard to not standarize when there's only one way to make mods apart from making your own exe as you described. tAPI uses jSon files, that's why I asked "Anybody up for learning some json?". I don't know if those use C or their own language, but I can safely say that it should be simple enough to port the ideas over there. Not the files, or the code, just the basic ideas of the mods.I looked into Terraria modding once, even though I haven't played the game a whole lot. It's written in C#. This means it's similar to Java in terms of being able to disassemble the game, but the process involved in actually doing so is a bit more complicated. The C# classes are embedded in the EXE, so even after you extract them, decompile them, repair the source code so that it'll recompile, etc, you then have to deal with getting the recompiled versions back into the EXE again.
I believe there's some modding APIs, but from what I saw there's not anything like the standardization available that there is for Minecraft. It feels far closer to what the Minecraft Pocket Edition community deals with.