Japanese fans have released the Japanese version of the game for the latest 1.2.2 version of TWOM. The full translation is available here:
http://whitecats.dip.jp/up2/download/1419881241.zip (pass is 111).
http://seesaawiki.jp/thiswarofmine/d/%c ... 8%ec%b2%bd - webpage of the project. This is really amazing work giving the complexity, amount of text and speed of the translation.
Installation:
Simply replace common.dat and common.idx in Steam > SteamApps > common > This War of Mine. You probably shuld make backups of original common.dat and common.idx as Japanese text replace English translation.
I guess the developers should contact the translation team and made this official part of the game. That is also another example how much game can benefit from modding and fan made assets.