Change language layout in screen lock

I have the exact same problem as you and I get around by doing this:

• get rid of gnome-screensaver by:

  sudo apt-get purge gnome-screensaver
  

• Install the X screensaver by:

  sudo apt-get install xscreensaver xscreensaver-data xscreensaver-gl
  

Whenever you forgot to switch back to English before the system locks itself, hit Ctrl+Alt+F1 log in as your admin user and kill -9 xscreensaver and you're back in!

(It's just a workaround and not a real "solution" but it works for me and is definitely better then shutting down and restarting)