SUMMARY
When trying to enter my password on the lock screen, I cannot enter a dead key (e.g. ', ", ^) or a special character (e.g. á, é, ö, û). My keyboard layout is English (US, intl., with dead keys), so this should in theory work. 

The keyboard layout does work once I am actually logged in (using the virtual keyboard).

STEPS TO REPRODUCE
1. Set keyboard layout to English (US, intl., with dead keys) in System Settings > Keyboard Settings.
2. Set user password to a string that contains accented characters and/or dead key characters.
3. Lock the screen and try to enter the password.

OBSERVED RESULT
Dead key characters and accented characters cannot be entered into the field, which makes logging in very difficult.

EXPECTED RESULT
The special characters should be registered properly which allows me to log in as expected.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kernel 4.19.49-1-MANJARO
(available in About System)
KDE Plasma Version: 5.15.5
KDE Frameworks Version: 5.59.0
Qt Version: 5.12.3

ADDITIONAL INFORMATION