Help! I changed my language on keyboard and I shut down my computer. Now keyboard doesn't work in English which I need to enter my password.
If you cannot access the Keyboard settings from the GUI, try running this command:
sudo dpkg-reconfigure keyboard-configuration
You can find more info here
To boot as root, at grub select "Advanced options for Ubuntu" then boot in "Recovery mode".
At the "Recovery Menu", you can choose "Drop to a root shell propmpt":
If your keyboard is working, although not in the correct keymap, you should be able to type the command.