One of my workmates has a custom layout created with the Microsoft Keyboard Layout Editor which has different caps lock/shift behaviour: if caps lock is on, it's a Dvorak layout, and if caps lock is off, it's QWERTY. Since caps lock is a global setting, hitting caps lock toggles between the layouts globally.
This is a horrible hack, it means you can't use your caps lock key normally, some programs use only the caps lock-off button for modified commands (e.g. Ctrl+C), and you can only use this with at most two layouts.
But, for all those disadvantages, it is a method of quickly changing globally between two different keyboard layouts.
Another option is to get a hardware converter/hardwired keyboard in the other layouts you want, and have multiple keyboards on your desktop, one for each language. That has its own set of disadvantages, though, namely having multiple keyboards on your desk and being at the whims of the (usually fairly limited) hardware rewiring.