Messages not honoring system locale

[brunosoli]

 * slick-greeter version 1.2.7
 * Distribution - Mint 19.2 with Mate desktop
 * VGA compatible controller, Intel Corporation Device 3e92, driver=i915
 * 64 bit

Issue
We have Mint configured to pt_BR locale and when a user is prompted to change his password (upon expiry), the messages are shown in english. We also have configured libpam-pwquality 1.4.0-2 and the messages regarding password quality are all in english too.

Using passwd on terminal all messages are correctly displayed in pt_BR.

Looks like slick-greeter has no language settings to force it to any given locale. So the questions are:

1. Are we missing something, is any further configuration needed?
2. Could it be lightdm related (as Mint 19.2 uses it)?
3. How can we debug/trace this issue?

Steps to reproduce

• Install linux Mint 19.2 with Mate desktop and select Brazilian Portuguese as locale;
• Not really needed: install and configure libpam-pwquality (default settings are enough);
• Force expire any user password;
• Try to login with that user to see the messages displayed in english.

We did not try with any other languages.

Expected behaviour
Upon expiry or password quality checks, the prompt in slick-greeter should display messages in system wide locale.

Other information

File /etc/lightdm/slick-greeter.conf content:

[Greeter]
background = /usr/share/backgrounds/cmc/login-bg.jpg
show-hostname=true
font-name=Ubuntu 18
activate-numlock=true

File /usr/share/lightdm/lightdm.conf.d/90-slick-greeter.conf content:

[Seat:*]
greeter-session=slick-greeter
greeter-show-manual-login=true
greeter-hide-users=true
greeter-setup-script=/usr/bin/numlockx

File /etc/default/locale content:

#  File generated by update-locale
LANG="pt_BR.UTF-8"
LANGUAGE="pt_BR:pt:en"

Output of locale command (same output to local users and root):

LANG=pt_BR.UTF-8
LANGUAGE=pt_BR:pt:en
LC_CTYPE="pt_BR.UTF-8"
LC_NUMERIC="pt_BR.UTF-8"
LC_TIME="pt_BR.UTF-8"
LC_COLLATE="pt_BR.UTF-8"
LC_MONETARY="pt_BR.UTF-8"
LC_MESSAGES="pt_BR.UTF-8"
LC_PAPER="pt_BR.UTF-8"
LC_NAME="pt_BR.UTF-8"
LC_ADDRESS="pt_BR.UTF-8"
LC_TELEPHONE="pt_BR.UTF-8"
LC_MEASUREMENT="pt_BR.UTF-8"
LC_IDENTIFICATION="pt_BR.UTF-8"
LC_ALL=

[github-actions]

This issue has been automatically marked as stale because it has not had
any activity in over 2 years.

If this issue is still relevant:

• Please test on a current version of this package.
• Add a comment with your findings

If no activity occurs in the next 30 days, this issue will be
automatically closed. Issues can be reopened if needed.

[brunosoli]

@Taresu, can you help us check if this issue still persists?