code: def relpath_to_site(lang, target_lang):
      '''Get relative path from siteurl of lang to siteurl of base_lang
  
      the output is cached in _SITES_RELPATH_DB
      '''
      path = _SITES_RELPATH_DB.get((lang, target_lang), None)
      if path is None:
          siteurl = _SITE_DB.get(lang, _MAIN_SITEURL)
          target_siteurl = _SITE_DB.get(target_lang, _MAIN_SITEURL)
          path = posixpath.relpath(get_site_path(target_siteurl),
                                   get_site_path(siteurl))
          _SITES_RELPATH_DB[(lang, target_lang)] = path
      return patf relpath_to_site(lang, target_lang):
      '''Get relative path from siteurl of lang to siteurl of base_lang
  
      the output is cached in _SITES_RELPATH_DB
      '''
      path = _SITES_RELPATH_DB.get((lang, target_lang), None)
      if path is None:
          siteurl = _SITE_DB.get(lang, _MAIN_SITEURL)
          target_siteurl = _SITE_DB.get(target_lang, _MAIN_SITEURL)
          path = posixpath.relpath(get_site_path(target_siteurl),
                                   get_site_path(siteurl))
          _SITES_RELPATH_DB[(lang, target_lang)] = path
      return path
docs: Get relative path from siteurl of lang to siteurl of base_lang
  
      the output is cached in _SITES_RELPATH_DB