gophers example and found that Japanese IME did not work. I understand this task would be hard and low priority, but I'd be happy if gio could support IMEs for other languages.
Thanks, This is definitely not low priority. It ties together with with general IME support which is crucial for non-toy use of Gio.
For reference, SDL supports this indirectly (at least on macOS) by having two separate events for input:
TextInputEvent for general input. It contains the actual string inputted, instead of just the keyboard's keycode.
TextEditingEvent for IME editing event. It contains the current text being edited by the IME.
Having something like this would have to be the first step to adding IME support.