First off, thank you for this great piece of software. Just what I was looking for!. I am attempting to standardize all my books to epub . I then use mobigen_linux to convert to a palm format. However it fails with an invalid language error. Inspection of the generated metadata.opf shows language as "Unknown". 
metadata:
    <metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns

pf="http://www.idpf.org/2007/opf">
        <dc:title>A Spell for Chameleon</dc:title>
        <dc:creator opf:role="aut">Piers Anthony</dc:creator>
        <dc:contributor opf:role="bkp" opf:files-as="calibre">calibre (0.4.91) [http://calibre.kovidgoyal.net]</dc:contributor>
        <dc:identifier opf:scheme="calibre" id="calibre_id">33a0bfae-ae76-4efa-9aaf-df9c9d842eac</dc:identifier>
        <dc:language>Unknown</dc:language>
        <dc

ublisher>DELREY</dc

ublisher>
        <series>Xanth</series>
        <series-index>1</series-index>
        <rating>5</rating>
        <dc:subject>fantasy</dc:subject>
    </metadata>
Is there a way to specify a language? I looked but found nothing. 2 items I noticed with the generated opf. I believe the elements series, series-index and rating should be placed inside meta tags as follows:
        <meta name="series" content="Xanth" />
        <meta name="series-index" content="1" />
        <meta name="rating" content="5" />
per 
http://www.openebook.org/2007/opf/OP...ec.html#TOC2.2
and in the element contributor the attribute files-as should be file-as.
I am a COBOL programmer (please, no dinosaur jokes!) but this project has me looking into python. Keep up the good work.