is a great open-source web chat developed using the Ajax technology and PHP as a server-side language. Download it here.

In short, the problem is that your script doesn't display the retrieved data correctly. For example, they are replaced by question marks, ?.

Putting this line of code at the beginning of your script might solve your problem:

Of course you'll have to change the charset value to match your needs.  Furthermore this might not be enough, you might also have to change the charset of the system your web application run into.
I hope this helps!