LXDE Raspberry language layout switching

Just put this command into your ~/.bashrc file:

setxkbmap -option grp:switch,grp:alt_shift_toggle,grp_led:scroll de,tr,us
Comments:

alt_shift_toggle can be replaced by another key combination.
grp_led:scroll is optional. Using it will turn on the scroll lock light if another layout than the first specified is active.
de,tr,us can be any comma-separated list of keyboard layouts. In this case German, Turkish, and US English layout.
Execute setxkbmap -option to reset these settings.