Anonymous Monk, thank you for the two suggestions.
I took a look at the InputLine.pm module and experimented with a few minor modifications of the on_keydown subroutine, but without luck.
I'm thinking the problem might be elsewhere. It doesn't seem to be an on_keydown event. Nor does it seem to be related to the wantUnicode property (I think the code generated through the IME on my system is not Unicode by default)
The thing is: even if I try to enter English words (latin letters) to the InputLine widget(or Edit widget) through the Chinese oriented Input Method Editor (IME) that can let me choose what to enter among a number of input candidates using the space or numerical keys on the keyboard, instead of directly entering characters found on the keyboard, I will fail. The InputLine widget seems to only accept inputs directly from the input device, ie the keyboard.
Thanks anyway :)