The accessibility plugin was modified to change the "lang" attribute set on paragraphs to "accessibility-lang", as the "lang" attribute wasn't interpreted by IE.
The changes were included in accessibility's html2xml.xsl but not in xml2htmleditor.xsl which still tries to copy a now inexisting "lang" attribute : the paragraph language is lost when editing a content.

To resolve this issue, maybe override docbook's xml2htmleditor.xsl in the plugin accessibility, as done with html2xml.xsl and then rewrite the "para" template to copy "accessibility-lang" instead of "lang".
Another solution would be to do this in the original docbook xml2htmleditor.xsl.

We'll probably have to take "lang" into account anyway to keep backward compatibility with contents created before the attribute name modification.