When having a file saved in ISO-8859-1 and using the command
echo "test: ".htmlspecialchars("äöü");
The return will be only "test: ".
This is because the standard charset for htmlspecialchars changed to UTF-8 in PHP5.4. You need to explicitly set the charset:
echo "test: ".htmlspecialchars("äöü", ENT_COMPAT | ENT_HTML401, 'ISO-8859-1');
Are there any other functions in PHP5.4, that will not work properly anymore, if you do not set the charset?