Firebug is your new best friend. Didn't you read the Mechanize FAQ or the Perlmonks archive? This sort of question comes up twice every month.

POST http://tools.webmasterei.com/mbrolatester/text2pho.php
Content-Length: 19
Content-Type: application/x-www-form-urlencoded; charset=UTF-8

foo=Gr%C3%BCnden&_=


200 OK
Content-Length: 98
Content-Type: text/html; charset=utf-8

gRYnd@n <script language="javascript">$('ipa').innerHTML='g&#641;&#655
+;nd&#601;n ';</script>
[download]