This will work in KDE. Open KDE Control Panel (Configure Your Desktop). Go to Hardware section > Input Devices. Keyboard in left pane, Layouts tab. Check the Configure layouts box. (Check for correct Keyboard model under the Hardware tab.) If you'd rather see a country flag than a language label, tick the Show flag radio button in the Layout Indicator section. Switching Policy is up to you. I left it at default Global. You can assign keyboard shortcuts.
Click the Add Layout button. In the Layout window:
Limit selection by language = Any language
Layout = (choose language)
Variant = Default
For Layout = (choose language), click the pull down menu and select the keyboard layout you want to add. You should probably ensure you have the locale installed in Synaptic for the keyboard layout additions you choose. Click Apply button.
You will now see a flag (or a language label) in the systray.
Click the flag (or label) to change your keyboard layout on the fly. I tried it with English (US) and English (UK). Below are shifted 1 through 5, first in US, then in UK.
XFCE and Gnome have similar settings, but I'm not sure what they are. For e17, LXDE and Openbox, you have to manually set up the keyboard layouts in CLI using setxkbmap. It's in our repositories. To use a graphical switcher that looks and works the same as the KDE one in e17, LXDE and Openbox, we need the fbxkb package, which is not in the repositories.