I got an answer with regards to the translation issue (threat: http://www.joomlart.com/forums/topic/how-to-change-language-ja-thumbnail/) but it does not fully solve my problem. Unfortunately, the thread was closed too quickly, so I am forced to open a new thread.
The problems I have are two-fold
1. I cannot find all the items I need to translate inside the file suggested above. So I can partially translate (see image 1 attached)
2. The popup that appears after clicking on the thumbnail, doubles the image count. Plus, I also need to translate this popup. Where is the translation file? I opened the japopup.ini file, but it is not there.