joomla/joomla-platform — pull request #727 by infograf768 (2012-01-09 07:45:46+00:00)
Title: *PHP 5.3.8 Notice for some language packs with iconv.

Notice: iconv() [function.iconv]: Detected an illegal character in input string in D:\wamp\www\j173\libraries\joomla\utilities\string.php on line 562 (error shown on 1.7.3, same on 2.5 beta)

Looks like an issue specific to that version of PHP. Tested with Cambodian language pack. I see no other solution atm than preventing the Notice display.