nix: Fix locales in development environment

[imincik]

Description

Fix locales in nix provided development environment.

Closes: #4503

Motivation and context

How has this been tested?

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to not work as before)

Checklist

• PR title provides summary of the changes and starts with one of the
  pre-defined prefixes

• My code follows the code style
  of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[wenzeslaus]

I successfully tested this locally earlier. I was actually suggesting you do it to ensure there is proper documentation of the change which I cannot do. I guess having it done by you is also a type of documentation :-)

[wenzeslaus]

Merged, thank you!