InputFix Mod allows you typing in-game using Input Methods for languages such as Japanese, Chinese and Korean.

Other Platforms (experimental):
To input a text in Mac and Linux, open up where you want to type, press F12, a input window should pop up, then type whatever you want.  btw, when input window is up, your game will stay not responding.
The whole F12 thing will simply not happen in Windows.
To disable the F12 thing, delete '\lain\mods\inputfix\impl\GuiScreenFixOthers.class' inside the jar file, this will cause the mod fallback to the windows routine.