Language translation fails

I installed Custom Properties 3 for Joomla 3.x and set the parameters.
CP 3 works functionally but language translation to Japanese fails.
I would appreciate it if anyone provide me any advice or suggestion to how to fix it.

Directory pass is as follows.
components\com_customproperties\language\ja-JP\index.html
components\com_customproperties\language\ja-JP\install.xml
components\com_customproperties\language\ja-JP\ja-JP.com_customproperties.ini
components\com_customproperties\language\ja-JP\ja-JP.xml

Thanks in advance

The file list you are referring to seems to belong to Custom Properties for J2.5.
IF my guessing is right, you probably carried out a 2.5 -> 3-x upgrade. And if that's the case, you should follow this procedure:
www.solidsystem.it/how-to-and-tutorials/...25-to-joomla-3x.html

This part:
--
Finalise Custom Properties upgrade
At this stage Custom Properties 3 is already installed, CP fields are there and the tags are still correctly assigned, but most of localized strings (i.e. menu, parameters, etc) are displayed incorrectly. Two operations need to be carried out manually.
1) delete the old language files, because CP 3 have them stored in a different place and the old one interferes. The files are: --
will fix the language issue.

I tried to follow your suggestion. Successful!
Thank you so much.