I have found some more information. This should be in the NXE README.
When reading document properties in the NXE server extension 8-bit characters are interpreted according to the platform’s default character set. This is fine as long as the document being stored in Tamino has been written on a platform with the same default character set. However, if you receive a document from another region of the world and want to process it with NXE you can not expect to get the correct indexing information - unless the creator used Unicode, of course.
#API-Management#webMethods-Tamino-XML-Server-APIs#webMethods