Pluralize Flag/Unflag Link Text
I found I was able to do this by changing the flag link text (in the flag configuration) to [node:flag-machinename-vote-count], which gave the number of flag for that node.

Then, modifying line 57 of the flag theme file: flag.tpl.php to

&lt;a href="&lt;?php print $link_href; ?&gt;" title="&lt;?php print $link_title; ?&gt;" class="&lt;?php print $flag_classes ?&gt;" rel="nofollow"&gt;&lt;?php print format_plural($link_text, '1 Flag', '@count Flags') ; ?&gt;&lt;/a&gt;&lt;span class="flag-throbber"&gt;&amp;nbsp;&lt;/span&gt;


Note that this is actually only changing the small php snippet that displays the link text to us the format_plural function:

this &lt;?php print $link_text; ?&gt;

to this &lt;?php print format_plural($link_text, '1 Flag', '@count Flags') ; ?&gt;