The most likely cause for this is an incorrect character set encoding in the XML file.
Version 2.72d and earlier
To resolve this problem, open the WebReportsLanguages.xml file in a text editor.
Open this file in a text editor, and adjust the encoding set in the first line of the file. By default, the first line will look similar to this:
<?xml version="1.0" encoding="ISO-8859-1"?>
For example, if you set the language to Korean, then you need to change the encoding type to EUC-KR, so the line would look like this:
<?xml version="1.0" encoding="EUC-KR"?>
Version 2.72e and later
Using the profile editor in the web reports (Maintenance - Profile Editor), specify a correct Encoding for your environment.
The web reports should then display correctly.