text/xml is for documents that would be meaningful to a human if presented as text without further processing, application/xml is for everything else
Every XML entity is suitable for use with the application/xml media type without modification. But this does not exploit the fact that XML can be treated as plain text in many cases. MIME user agents (and web user agents) that do not have explicit support for application/xml will treat it as application/octet-stream, for example, by offering to save it to a file.
To indicate that an XML entity should be treated as plain text by default, use the text/xml media type. This restricts the encoding used in the XML entity to those that are compatible with the requirements for text media types as described in [RFC-2045] and [RFC-2046], e.g., UTF-8, but not UTF-16 (except for HTTP).