Comment 208 for bug 1245473

Found partial workaround today.

It _is_ possible to setup xkb so that the group (i.e. layout) switch occurs on <Shift>+<Alt> (which means press and hold Shift, then press Alt - order matters) - and still <Alt>+<Shift>+<something> (first alt, then shift, then something) shortcuts work. All this without the need to recompile xserver.

Here's what I did:

$ setxkbmap us,cz
(just load the layouts I want to the server, switching not working yet)
$ xkbcomp $DISPLAY xkbdesc
(list the xkb description from server to a file named "xkbdesc")

Now two little changes to xkbdesc:

change1:

     key <LALT> { [ Alt_L, Meta_L ] };
to
     key <LALT> { [ Alt_L, ISO_Next_Group ] };

change2:

      key <RALT> {
          type[group1]= "TWO_LEVEL",
         type[group2]= "ONE_LEVEL",
         symbols[Group1]= [ Alt_R, Meta_R ],
         symbols[Group2]= [ ISO_Level3_Shift ]
      };
to
      key <RALT> {
          type[group1]= "TWO_LEVEL",
         type[group2]= "TWO_LEVEL",
         symbols[Group1]= [ Alt_R, ISO_Next_Group ],
         symbols[Group2]= [ ISO_Level3_Shift, ISO_Next_Group ]
      };

then
$ xkbcomp xkbdesc $DISPLAY
(load kbdesc to the server; ignore the warnings)

and voila! Shift+Alt (in that order) switches us<->cz keyboard and Alt+Shift+Tab works like it should.

I was actually quite surprised when I found this.

PS: Next time you start X, you can do just the last step, supposed you keep the xkbdesc file.