code: function handleLocaleSubdomains( req, res, next ) {
  	const langSlug = endsWith( req.hostname, config( 'hostname' ) )
  		? split( req.hostname, '.' )[ 0 ]
  		: null;
  
  	if ( langSlug && includes( config( 'magnificent_non_en_locales' ), langSlug ) ) {
  		// Retrieve the language object for the RTL information.
  		const language = getLanguage( langSlug );
  
  		// Switch locales only in a logged-out state.
  		if ( language && ! req.context.isLoggedIn ) {
  			req.context = {
  				...req.context,
  				lang: language.langSlug,
  				isRTL: !! language.rtl,
  			};
  		} else {
  			// Strip the langSlug and redirect using hostname
  			// so that the user's locale preferences take priority.
  			const protocol = req.get( 'X-Forwarded-Proto' ) === 'https' ? 'https' : 'http';
  			const port = process.env.PORT || config( 'port' ) || '';
  			const hostname = req.hostname.substr( langSlug.length + 1 );
  			const redirectUrl = `${ protocol }://${ hostname }:${ port }${ req.path }`;
  			return res.redirect( redirectUrl );
  		}
  	}
  	next();
  }
docs: Sets language properties to context if
  a WordPress.com language slug is detected in the hostname
  
  @param {Object} req Express request object
  @param {Object} res Express response object
  @param {Function} next a callback to call when done
  @returns {Function|Undefined} res.redirect if not logged in