If you want to switch between keyboard mappings, you need to add a setxkbmap command to /etc/xdg/lxsession/Lubuntu/autostart
To switch between two keyboard mappings with the control+shift keys, Open the terminal and
echo '@setxkbmap -option grp:ctrl_shift_toggle "de,us"' | sudo tee -a /etc/xdg/lxsession/Lubuntu/autostart
Keyboard mapping for 13.10 and beyond
Since Lubuntu 13.10, the method to choose and toggle keyboard layout has changed. Indeed, lxkeymap application is no longer installed by default, and we have to use Keyboard Layout Handler instead, a plugin for lxpanel.
On Lubuntu default installation, Keyboard Layout Handler appears on the right of the panel, near volume control. It displays a box which describes the current keyboard layout (for example, “US”). To modify keyboard layout settings, right click on it, and choose « Keyboard Layout Handler Settings ». Here you can make some modifications.
By default, the option « Keep system layouts » is checked. Uncheck it to customize your keyboard layout.
source: Lubuntu community/Keyboard