wordpressPackages: Add German plugin translations

[onny]

Description of changes

Adding translation German translation files to plugin packages.

Tested it with:

{ pkgs, ... }:{

  services.wordpress.sites."localhost" = {
    themes = {
      inherit (pkgs.wordpressPackages.themes)
        twentytwentythree;
    };
    plugins = {
      inherit (pkgs.wordpressPackages.plugins)
        jetpack;
    };
    languages = [ pkgs.wordpressPackages.languages.de_DE ];
    settings = {
      WPLANG = "de_DE";
      JETPACK_DEV_DEBUG = true;
    };
  };

}

Fixes helsinki-systems/wp4nix#2

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[onny]

@mohe2015 I saw that translation files for Wordpress plugins were missing. I did some research on how it works and trying to implement packaging here helsinki-systems/wp4nix#2

I would like to have an additional plugin package output "i18l" where the plugin translation files are located