I am using EditTime at the moment: it supports Unicode document character set
and ENR extended naming rules SGML declaration. It is not officially XML,
but you can type in /> for EMPTY elements, so you can create XML documents.
I don't know whether it allows &#x hexadecimal numeric character references,
but it certainly supports SPREAD-style &U hexadeclimal entity references, so
it can be trivially converted to XML.
They seem to have Japanese & Chinese versions available, and also support the
European scripts.
Rick Jelliffe