How does one install and test Windows locales in support of `set locale()` in the GitHub Windows runner?

Question

I've added tests for localization to Sqitch, which requires that the POSIX setlocale() function return an appropriate value. A couple of GitHub workflows run this tests on Linux, macOS, and Windows, and work fine. On Linux, the workflow has to install the locales for the tests to pass:

- if: runner.os == 'Linux'
  name: Install Apt Packages
  run: sudo apt-get install -qq language-pack-fr language-pack-en language-pack-de language-pack-it

The tests, however, fail on Windows. The warning emitted when it tries to set the locale to en-US.UTF-8 is:

perl: warning: Please check that your locale settings:
    LC_ALL = "en-US.UTF-8",
    (possibly more locale environment variables)
    LANG = (unset)
    are supported and installed on your system.
perl: warning: Falling back to the system default locale ("English_United States.1252").

I suspect that this error is not a Perl issue, since Perl, IIUC, delegates to the Windows setlocale function, which explicitly documents support for the LC_ALL environment variable and the en-US.UTF-8 format.

I had similar issues on Linux till I figured out how to apt-get install the locales, and suspect a lack of localization libraries on the GitHub Windows runner. I tried to install them with this incantation:

- if: runner.os == 'Windows'
  name: Install Language Packs
  run: |
    Install-Language -Language en-US
    Install-Language -Language fr-FR
    Install-Language -Language de-DE
    Install-Language -Language it-IT

But the build fails with

The term 'Install-Language' is not recognized as a name of a cmdlet, function, script file, or executable

I assume this is because Install-Language requires admin access.

So, how does one install localization languages on the GitHub Windows runner? The goal is for a workflow like this:

name: Test setlocale
on: [push]
jobs:
  test:
    name: Test setlocale
    runs-on: windows-latest
    steps:
      - uses: actions/checkout@v4
      - uses: shogo82148/actions-setup-perl@v1
        with: { perl-version: latest }
      - run: Install-Language -Language fr-FR
      - run: perl -MPOSIX -E "say POSIX::setlocale(POSIX::LC_ALL)"
        env: { LC_ALL: fr_FR.UTF-8 }

to emit fr_FR.UTF-8.

I also put together this simple test case, which currently fails.