Minetest and IBus cause issues with Cyrillic text
This issue is linked to the following issue in Minetest itself.
When IBus is active (e.g. when a CJK layout using it is added into GNOME), typing Cyrillic text into Minetest causes it to display as a mix of unrelated Chinese and Korean characters.
A partial workaround for this issue would be to build Minetest's Irrlicht engine with SDL2 support -- while CJK input still doesn't work, Cyrillic now does.
After some experimenting, I have supplied some patch files that would enable IrrlichtMT (Minetest's version of the engine) to be built with SDL2 support.