After entering the game, every time I start a conversation box then change my input method (English => Chinese Traditional [CantoHK]) using ibus short-cut key alt+space and type some text, my character cannot attack any target.
I can still move the character, summoning mounts and perform all other non-attacking moves
Maybe pressing alt toggles some behaviour in the game (or it doesn’t recognize you’ve let go of the key)?
If you can, try to disable the IME switcher and see if the issue persists when using the same keystroke.
It works after I press alt again…weird 
thanks a lot 
In general case, that’s a widespread problem with keystroke/mouseclick detection; if the end event (keyup) was processed by a different program (or even different part of the same), the one which handled the start event (keydown) doesn’t know the key/mouse button isn’t pressed anymore.