declare namespace functx = "http://www.functx.com";
declare function functx:format-as-title-en
  ( $titles as xs:string* )  as xs:string* {

   let $wordsToMoveToEnd := ('A', 'An', 'The')
   for $title in $titles
   let $firstWord := functx:substring-before-match($title,'\W')
   return if ($firstWord = $wordsToMoveToEnd)
          then replace($title,'(.*?)\W(.*)', '$2, $1')
          else $title
 } ;

functx:format-as-title-en(
     ('A Midsummer Night''s Dream',
      'The Merchant of Venice',
      'Hamlet'))

('Midsummer Night's Dream, A',
 'Merchant of Venice, The',
 'Hamlet'''Midsummer Night's Dream, A',
 'Merchant of Venice, The',
 'Hamlet')