GoldenDict is almost THE perfect dictionary software. I really thank you geniuses who contributed enormous time and effort to this project.
As a Japanese learner, I use EBWin ( http://ebstudio.info/manual/EBWin4/EBWin4.html ) most of the time. There're tons of excellent EPWING format dictionaries, eg.
I noticed some guys had already made the request of EPWING support, which I have also been looking forward to eagerly. The link here https://github.com/goldendict/goldendict/issues/298 offered some useful information. I'll add some other information which may be helpful.
1. Here is a list of software which supports EPWING http://rtkwiki.koohii.com/wiki/EPWING_software
Among them, EBView and qolibri are open-source.
EBView: http://ebview.sourceforge.net/
qolibri: http://qolibri.sourceforge.jp/
2. Rikaisama http://rikaisama.sourceforge.net/index.html
This is a really cool Firefox add-on which supports EPWING. Another good point is that it's also open-source. see http://sourceforge.net/projects/rikaisama/files/
Hope these are useful. Thank you again.