Hi, 

I use en_US.utf8 and es_ES.utf8 locales on the same system. LightDM has a
locale selector, but the selected locale does not take effect until after a
system reboot. 

For example, I log in the first time with en_US, log out, and for the same user
I select "Spanish (Spain)" in LightDM. However upon logging in, the interface
is still in English, and the environment variable LANG=en_US.utf8 is still set.
Then if I reboot and log in, the interface will finally be in Spanish. However,
if I log out and change it back to en_US, the interface will remain in Spanish
until the next reboot.

I also tried switching between different user accounts, and I also tried
killing the X server with Ctrl+Alt+Bksp, but it makes no difference.

I tried both the official Leap version as well as the X11:Utilities repo
versions of lightdm and lightdm-gtk-greeter, but the bug remains.