In Windows is Shift+Alt to change keyboard (example- English to Slovak). Is in Ubuntu it? And where?
just press right alt button. You can switch on input methods.
But before that, you should open iBus ( a input method selecting program) and set your languages using it's preferences.
If you can't see any language installed: You have install m17n-engine using synaptic package manager. For that you can simply search as 'm17n' in search field of synaptic package manager
after that you can switch in to you languages using preferences category of iBus .
When you start the application once, it will automatically start at every login. So, at typing just press right alt button and switch between input methods.