I'm slowly skimming the Papyrix ereader firmware, and... Nice! It includes a bare-metal international text-renderer, targetting a memory-constrained RISC32i microcontroller & eink display!
To achieve this it uses its own (raster) font file-format, with special handling for Arabic, Thai, & Chinese/Japanese/Korean. Naturally there's a script to rasterize normal fonts.
So now all I need to test my concept for mobile typing is... Someone (ideally local) to team up with on the hardware!