When source file is XML, 'Document' -> 'Preview translation' in the Editors returns an HTML file (transformed from the XML with the default or custom XSLT).
Available workaround (if any):
To get an XML file, users can rename the HTML to XML as it is actually in XML format.
An option to choose the desired file format (extension).
Sometimes, users have a working environment where XML input is needed. HTML is convenient for opening in a browser, but in other cases, renaming is an extra step that could be avoided with this feature.
When source file is XML, option to download XML from 'Document' -> 'Preview translation'