Add an easy way to change language for the live session

[kurkha]

For some users not speaking english, having an easier way to change language for the live session would be useful and sometimes even mandatory – how do you dare to install a system when you cannot really test it because you don't understand its language?

Simplest way to implement this, at least partially: add the shortcut to language settings to live session desktop. There is a problem, though, i.e. actually changing the interface language requires a logout and login. Any suggestions for this?

Also, easy way of changing keyboard layout would also be nice, but this is a more complicated matter.