[CentOS] Where should my Xdefaults file be?

Apparently in order to get Japanese input working, I need to edit my 
Xdefaults file.

By hunting on the web, I've read that I can create my own Xdefaults 
file, but it's been very difficult to determine where I should create it.

I simply want to add the following line to this file:
*inputMethod kinput2

... so that Japanese input will be enabled. I want this setting to be 
global for all users of my machine (which is only me, but just in case).

So where is, or where should be, my Xdefaults file?

Just in case anyone wants to know where I got this idea from, I got it 
from here:
http://laeren.zoggins.net/japan/japanmoz.shtml

Thanks