The reason is quite simple: those characters belong in the Unicode [
#] encoding, while SMF uses the heavily outdated Latin-1 [
#] encoding, which is not advised for usage for these particular reasons. Perhaps a slight change in the application code could enable that the pages are served encoded as Unicode rather than Latin-1, something in line of:
<?php
header("Content-type: text/html; charset=utf-8");
?>And also setting a proper encoding in the HTML.