When search people by Korean on global search or assign, it is impossible to use auto complete.
But some people could be search by Korean. I don't know why. ( search normal user as an administrator )
After search by English, it changed to be possible to find by Korean. After refresh page, it changed to be impossible again.
And found another state. After make administrator an user, I can search by Korean forever(may be - after refresh).
It remain after remove administrator. Maybe there are some process for that.