Steps to reproduce

1. Add a date custom field
2. Ensure that the database, file encoding and application server are all using the utf-8 encoding as per the guide in page
3. Change the default language of your JIRA instance to French for example
4. Choose a sample issue and set the value of the new custom field to "1 February 2012" (in french 1er février 2012)
5. Display the updated issue in the navigator
   
6. click on the view/xml menu
   
7. The browser displays this error message
   

The problem is probably due to the fact that com.atlassian.jira.datetime.DateTimeVelocityUtils.formatRSS(Date) method referenced in xml-date.vm does not escape accented characters in a consistent manner.