$ sudo apt-get update
$ sudo apt-get install latex-cjk-japanese 

latex-cjk-japanese is installed in your system.

Make ensure the latex-cjk-japanese package were installed using the commands given below,

$ sudo dpkg-query -l | grep latex-cjk-japanese *

You will get with latex-cjk-japanese package name, version, architecture and description in a table

latex-cjk-japanese package basic information: