I am using your tool quite regularly and like it.
Sadly, there is no support for krautchan.net which is a German chan I visit some times.
Because of this, I wrote a plugin for it.
It would be great if you could add this to the next official release.
The changes are available at https://github.com/J0s3f/fourchan-dl/commit/ddc00f348e519525356bcba6ca0d6a0a7c936635
I have only Qt5 at this PC and was doing the development using that, so I haven't actually tested this with Qt4, but it should work.
I will probably keep this plugin updated, so if somebody complains it is broken, there might be a working version at my github. (I will most likely support a bug report here, but I might forget it)