Just discovered THE way (another forum) to do it in KDE4. How could I miss it?
1- KDE control panel
2- Icon regional and languages (blue flag)
3- Keyboard layout
- tick "activate keyboard layout"
- drag the desired keyboard layouts to the right column
4- click apply
Now in the taskbar you have a flag of the active keyboard layout
JUST CLICK ON IT TO TOGGLE TO ANOTHER LAYOUT!!!