Our hotkey system is a little barebones and inflexible. Changes to SDL2 have made it impossible to use some keys on some keyboards (e.g. French keyboards, can't use accents for any hotkey).
It would be nice to completely overhaul it, but in the meantime I would suggest adding a call to SDL_GetKeyFromName to try and recognise an unknown mapping. This fixes the issue on my keyboard and allows me to setup hotkeys I want.