Very nice results!

Thank you

Is it a room created in Sweet Home 3D, then imported into Blender and Yafaray?

Exactly. However, there were some minor things to tweak - missing sun, sky light setup, and I think I had to change the glass material in the windows. I also played with the walls material. On a sidenote - I know SH3D cannot export sun position to the OBJ file, but maybe some sort of a dummy object could be placed just to mark the coordinates ?
Also, the imported mesh is very small in the blender viewport - scaling is necessary. Yesterday I estimated that to have 1 metre from the original SH3D project correspond to 1 blender unit the mesh has to be rescaled by a factor of about 14.84.

My main problem about trying other solutions is time!

I know what you're talking about I'm a pro programmer myself, and I rarely have time to develop sth besides that.

As SunFlow isn't really maintained anymore, I even wondered if I shouldn't have better translate from Yafaray into Java.

Translating C/C++ to Java ? Please, don't, performance will deteriorate significantly. I'm not a java expert, maybe it would be just sufficient to provide a similar solution just like in blender - having an export plugin to the standalone yafaray binary executable ?

You should also notice that many users are satisfied by the current result and expect more new features like multiple levels and roof management, than a better rendering.

Well, let's hope that power of Open Source will kick in and you'll find a helping hand.

A first approach could be to develop a plug-in able to translate Sweet Home 3D / Java 3D data in a format supported by Yafaray (you can have a look to OBJWriter and PhotoRenderer classes to get ideas), then launch Yafaray renderer with the exec method of the Runtime class. Who wants to try?

I thought about it. Right now I'm additionally busy with arranging my new appartment - that's why SH3D found my desktop But who knows.. I don't want to promise anything.