Thank you for your quick reply.

1.The Japanese language pack is for the both side.
I didn't change the data base by SQL.
I changed default language from the main screen.
I intend to remove the Japanese language pack and test again.

2.After installing the Japanese language pack, I changed the default language to Japanese.
English language is still present and it's language_id is 1. I didn't touch about English.
----------the information on the main screen of tools->Easy Populate v4---------------
Easy Populate 4.0.37.6 - 02-08-2017
Installed Languages
2-ja: Japanese
1-en: English
Default Language: 2-Japanese
Internal Character Encoding: UTF-8
DB Collation: utf8
--------------------------------------------------------------------------------------

3. I will try https://github.com/mc12345678/EasyPopulate-4.0 .

4. I think this message is regarding 'roducts_model:', but I don't know how to solve it because of my limited ability.

I will try what I can.
Thank you.