discourse/app/models/locale_site_setting.rb

require_dependency 'enum_site_setting'

class LocaleSiteSetting < EnumSiteSetting

  def self.valid_value?(val)
    supported_locales.include?(val)
  end

  def self.values
    @values ||= supported_locales.map do |locale|
      lang = language_names[locale] || language_names[locale.split("_")[0]]
      {
        name: lang ? lang['nativeName'] : locale,
        value: locale
      }
    end
  end

  @lock = Mutex.new

  def self.language_names
    return @language_names if @language_names

    @lock.synchronize do
      @language_names ||= begin
        names = YAML.load(File.read(File.join(Rails.root, 'config', 'locales', 'names.yml')))

        DiscoursePluginRegistry.locales.each do |locale, options|
          if !names.key?(locale) && options[:name] && options[:nativeName]
            names[locale] = { "name" => options[:name], "nativeName" => options[:nativeName] }
          end
        end

        names
      end
    end
  end

  def self.supported_locales
    @lock.synchronize do
      @supported_locales ||= begin
        locales = Dir.glob(
          File.join(Rails.root, 'config', 'locales', 'client.*.yml')
        ).map { |x| x.split('.')[-2] }

        locales += DiscoursePluginRegistry.locales.keys
        locales.uniq.sort
      end
    end
  end

  def self.reset!
    @lock.synchronize do
      @values = @language_names = @supported_locales = nil
    end
  end

  def self.fallback_locale(locale)
    plugin_locale = DiscoursePluginRegistry.locales[locale.to_s]
    plugin_locale ? plugin_locale[:fallbackLocale]&.to_sym : nil
  end
end