I found a simple solution thanks to this answer:
[How do I change the singular/plural on “comment” to “comments” on Facebook's number of comments?][1]

Here is how I solved without the <fb> tag, using the code I was already working for, this goes into function.php

    function get_likes($url) {
       $json_string = file_get_contents('http://graph.facebook.com/?ids=' . $url);
       $json = json_decode($json_string, true);
       $count = intval( $json[$url]['shares'] );
       if ($count == 0) {
         echo "share!";
       } elseif ($count == 1) {
         echo "shared 1 time";
       } else {
       echo "$count shares";
       }
    } 

and this in the template

    <?php $url = get_permalink( $post_id ); echo get_likes($url); ?>

  [1]: http://stackoverflow.com/questions/8286964/how-do-i-change-the-singular-plural-on-comment-to-comments-on-facebooks-num