Why are special chars not displayed correctly on my Debian systems?

Since the release of Etch, Debian uses UTF-8 as default charset. For now most parts of the source code are not written in UTF-8. You can change the default charset back to its previous default by modifying /etc/apache2/apache2.conf

AddDefaultCharset ISO-8859-1

Restart your Apache after this change.

This issue seems to be fixed in the latest version of ispCP.