Login screen password language
There is an alternative solution for the problem. You can disable all languages system-wide, except English, but leave the languages for your current user. I'm using Ubuntu 17.10.
- Go to Settings -> Region & Language -> Manage Installed Languages.
Remove all languages using "Install / Remove Languages..." button, except English (only "русский" in my case).
Apply settings system-wide.
Re-install languages that were removed on step 2.
This is still an issue on Ubuntu 18.04. None of the answers above worked for me so I've created this mini package to fix the problem
https://github.com/Idan-/magicLockLayout
Please read the instructions first.