missing language in the selection list

I missed Japanese language from my language bar recently which I had used for

long time.

To figure out the problem, I went to:

control panel-->regional and language options-->tab of "keyboards and

languages"-->click "change keyboards"-->tab of "general"-->check "installed

services"

I found there was no Japanese in the list.

Then I continued to:

click "add"-->try to select from the list

However, suprisingly, there was no Japanese in the list either!

Anybody can kindly help me to solve this problem?

Thanks a lot.