Shows how to generate sitemap with sitemap_generator gem for multilingual site and set rewrite urls in nginx conf.

nginx-site.conf

rewrite ^/sitemap1.xml.gz /sitemaps/$host/sitemap1.xml.gz last;
rewrite ^/sitemap_index.xml.gz /sitemaps/$host/sitemap_index.xml.gz last;

# or 

    location /sitemap {
        # it can be already switched on for globally
        # gzip_static on;

        rewrite ^/sitemap.xml /sitemaps/$host/sitemap.xml last; # that's will catch .gz files and served as normal static file, but with gzip header
    }

sitemap.rb

require 'rubygems'
require 'sitemap_generator'

# Constants::HOSTS = {'www.site.com' => :en, 'www.site.de' => :de}

Constants::HOSTS.each do |host, locale|
  SitemapGenerator::Sitemap.default_host = "http://#{host}"


  SitemapGenerator::Sitemap.public_path = "public/sitemaps/#{host}"
  SitemapGenerator::Sitemap.sitemaps_path = ''


  SitemapGenerator::Sitemap.create do
    add root_path, priority: 1

    Property.find_each do |property|
      add property_path(property),
          priority: 0.8,
          lastmod: (property.updated_at || property.created_at),
          alternates: Constants::HOSTS.map { |h, l|
            if locale != l
              {
                href: property_url(property, host: h),
                lang: l
              }
            end
          }.compact
    end


  end

  SitemapGenerator::Sitemap.ping_search_engines
end