According to https://github.com/goldendict/goldendict/issues/183, upstream has provided a high resolution icon. But I still have the old ugly icon in my system even with 9999.
pinkbyte@phantom ~ $ file /usr/share/pixmaps/goldendict.png /usr/share/pixmaps/goldendict.png: PNG image data, 24 x 24, 8-bit/color RGBA, non-interlaced According to commit log - icon is changed only in application, buildsystem still installs 24x24 pixmap, used in desktop file. There is not our fault - ask upstream to install high resolution pixmap too.