How to add new language to Android phone?

I have an android phone (Samsung S4). I want to add Japanese language to my phone. I don’t know why the hell Samsung have not added Japanese language support for the phone. Phone has sibling languages, like Chinese, and Korean. But no Japanese.
Is there any way by which I can add a new language to my phone?
*(I do not want Japanese as an input language. I am looking for new language for my entire phone)
Answer #1
Koreans hate the Japanese greater than Chinese. Plus Japanese has too many language symbols, this makes inplementing more expensive.
A rom flash may work.
I suspect there may only be carrier locked roms from ntt.
Answer #2
All you need to do is install an android app called Morelocale. You can find it here: https://market.android.com/details?id=jp.co.c_lis.ccl.morelocale
Answer #3
All you need to do is install an android app called Morelocale. You can find it here: https://market.android.com/details?id=jp.co.c_lis.ccl.morelocale
That worked quite well.
Thank you.
But, for MoreLocale to run, phone must be rooted.
Answer #4
that’s bollocks. It doesn’t have to be rooted