Please check your Japanese translation with the English version e.g. in Notepad.
All strings of the English version should be translated and substituted (taking care also that no "double strings" appear under the same number like I saw).
If you then use Japanese language in BSPlayer and some English strings are still shown e.g. (repeat) search these strings in Notepad in the English version and then check if they are in your Japanese translation.
Success from a fellow user and translator of BSPlayer!!