The original post is OK but the quoted characters are mixed up only?
There is a line in the quote plugin that converts all special characters to their HTML equivalents.
if ($row) echo htmlentities('<blockquote>'.$row->post_text.'</blockquote>');
(Some code is cut off to the side because of the forum’s limited width) I assume that the problem lies here. My guess is that it returns a different character format to the one your browser is using?
Get your quote.php file in your plugin folder and change this code to
if ($row) echo htmlentities('<blockquote>'.$row->post_text.'</blockquote>', ENT_COMPAT, 'UTF-8');
Upload the new version to your server and see if it works. If not, undo changes, save and upload the original file.
That’s just my guess; the first thing I would try. I don’t actually know.
Thanks also – I’ve updated the plugin and tagged 0.2.