Content language
Capture each primary language of a book in a content-language element.
Identify a language by a single value, lower-case code from the IANA language subtag type list .
Capture a content-language element once for each language used in the document.
For monolingual books (i.e., if no additional primary languages are provided), capture exactly one content-language element. Capture its content as the code used as the value for the xml:lang attribute at the book root element.
For multilingual books (i.e., if two or more primary languages are provided), capture at least one content-language element whose content matches the code used as the value for the xml:lang attribute at the book root element.
Monolingual book
<book xmlns:mml="http://www.w3.org/1998/Math/MathML"
xmlns:xlink="http://www.w3.org/1999/xlink" xml:lang="fr">
<!-- additional elements inserted -->
<book-meta>
<!-- additional elements inserted -->
<content-language>fr</content-language>
</book-meta>
</book>
Multilingual book
<book xmlns:mml="http://www.w3.org/1998/Math/MathML"
xmlns:xlink="http://www.w3.org/1999/xlink" xml:lang="en">
<!-- additional elements inserted -->
<book-meta>
<!-- additional elements inserted -->
<content-language>en</content-language>
<content-language>fr</content-language>
<content-language>de</content-language>
</book-meta>
</book>