It is not debug.log but also this screen shows incorrect settings.
Setting the audio preference and sub preference is ignored when you will set *,* in audio/sub preference because this line is preferred. *,* means play any subs for any audio what is not what we wants.
Change it to e.g. en,off which means disabling subs for English audio if present.
Then your separate subs setting will not be ignored.
But the best way is to set audio/sub combination only.
So if en is your native language but not jp you should set eg.:
It means for en audio disable subs, but if not present try to load en subs for jpn audio. If none of them found, disable subs for any audio (*).
Above is only an example how the logic works.
This logic works only when MEncoder engine is used, it means file is transcoded/reencoded. It is only solution how to display subs,burn them in video.
2char and 3char lang codes:http://en.m.wikipedia.org/wiki/List_of_ISO_639-1_codes