The W3C has released an updated working draft of "Best Practices for XML Internationalization", which has been authored by the Internationalization Tag Set (ITS) Working Group.
This document is a complement to the W3C Recommendation Internationalization Tag Set (ITS). However, not all internationalization-related issues can be resolved by the special markup described in ITS. The best practices in the new working draft document, therefore, go beyond application of ITS markup to address a number of problems that can be avoided by correctly designing XML schemas, and by applying a few additional guidelines when writing XML content in an XML editor.
See also this announcement on the W3C Internationalization (I18n) Blog.