Hello! I use Diasy as my dock and do not use system tray because i have no place for it. But not having keyboard layout indicator is annoying. So I am going to write simple sqaure plasmoid to show current layout(I use 3 - Rus, Eng and Greek). So my question is how get current layot using KDELibs without
reading a lot of KDE sources.

I would recommend starting by reading the existing Keyboard Layout application sources.
Before you do this however, you are aware that the System Tray can hide all the icons you do not want to see right?