This problem happened long time ago , At All Minecraft Version (e.g Minecraft 1.5,1.6,1.7,1.8) (OS : Win7,Win8,Win10), you want to chat by using Traditional Chinese characters , Simplified Chinese characters Or
Japanese language , you can't type at chat bar ,
Well , there are a two way to fix it .
1. You can Typing the Word at other place , and Copy & Paste to the Minecraft Chat Bar.
2.You can use a Mod Call InPutFix : http://www.curse.com/mc-mods/minecraft/inputfix

But , It's very inconvenient , e.g , mod update need a lots of time , e.g , there is a only 1.8 forge , when you want to use InPutFix Mod to type Words, you can't use 1.8.1 1.8.2 etc..
So , you can just use 1.8 to play Or just by using Copy&Paste

So, I don't know is it hard to fix it , but, I just want minecraft can Support typing Traditional Chinese characters.. that we don't need to add any mod .

Well, this is a very common problem around the asia countries who use the Traditional Chinese characters , you can search "minecraft Inputfix" there are many article about it , if mojang can fix this problem that we don't need to add any mod , it will a big big awesome thing for all hongkong / Taiwan .... Minecraft player . Well , I am a hongkonger , I am a big fans of Minecraft (I have 2 Minecraft AC , One for me to play , One of me to testing Or Share the Ac to friends that don't have Minecraft Ac ,but want to try to play Minecraft ) Also , I have a Minecraft Realms, Minecraft Realms need you to use most recently Minecraft Version , So I can't use 1.8 Forge (InPutFix) to play minecraft . So , during I playing minigame at realms , I can't type any word on minecraft , because Copy&Paste Need too many time . So , I hope that Minecraft can support typing Chinese Words .