Comment 3 for bug 877671

Only tried with lightdm. There is no way to change the keyboard layout on the logon screen and there is no direct indication of the current layout.

This is a regression from the blueprint from Matt Zimmerman which dates back from 2005 :
https://blueprints.launchpad.net/ubuntu/+spec/gdm-keyboard-layout

    As of Ubuntu 5.10, the initial keyboard layout used before login is part of the X.org configuration file,
     and cannot be adjusted by the user until after login. This is problematic because:

    The user may not be able to login if the layout is incorrect

    The X keyboard layout is currently "guessed" from the console layout chosen in the installer,
    and this process is known to be imperfect

    Different users may require different keyboard layouts

    This requires that the keyboard layout be asked for ahead of time on the live CD,
    which is inconvenient for the user