xml:lang 

<div>
  <h3>lang (as an attribute name)</h3>
  <p>denotes an attribute whose value is a language code for the natural language of the content of any element; its value is inherited. This name is reserved by virtue of its definition in the XML specification.</p>
</div>
<div>
  <h4>Notes</h4>
  <p>Attempting to install the relevant ISO 2- and 3-letter codes as the enumerated possible values is probably never going to be a realistic possibility.</p>
  <p>See BCP 47 at
    <a href="http://www.rfc-editor.org/rfc/bcp/bcp47.txt">http://www.rfc-editor.org/rfc/bcp/bcp47.txt</a>and the IANA language subtag registry at
    <a href="http://www.iana.org/assignments/language-subtag-registry">http://www.iana.org/assignments/language-subtag-registry</a>for further information.</p>
  <p>The union allows for the 'un-declaration' of xml:lang with the empty string.</p>
</div>

Attribute Information

Used By

Attribute Group xml:specialAttrs
Elements abbrev, abbrev-journal-title, abstract, ack, addr-line, address, aff, alt-text, alt-title, annotation, anonymous, app, app-group, array, article, article-title, attrib, author-comment, award-group, award-id, bio, boxed-text, caption, chapter-title, chem-struct, chem-struct-wrap, city, code, collab, comment, conf-acronym, conf-date, conf-loc, conf-name, conf-num, conf-sponsor, conf-theme, conference, contrib-id, copyright-holder, copyright-statement, corresp, country, custom-meta, data-title, date-in-citation, day, def, def-item, def-list, degrees, disp-formula, disp-formula-group, disp-quote, edition, element-citation, email, era, etal, ext-link, fig, fig-group, fn, fn-group, fpage, funding-group, funding-source, funding-statement, glossary, gov, graphic, inline-formula, inline-graphic, inline-supplementary-material, institution, institution-id, issue, issue-id, issue-part, issue-sponsor, issue-title, journal-id, journal-subtitle, journal-title, kwd-group, label, license, list, list-item, long-desc, lpage, media, milestone-end, milestone-start, mixed-citation, month, name, named-content, nlm-citation, note, notes, on-behalf-of, open-access, p, page-range, part-title, patent, person-group, postal-code, prefix, preformat, price, principal-award-recipient, principal-investigator, product, pub-date, publisher-loc, publisher-name, rb, ref, ref-list, related-article, related-object, response, role, rt, season, sec, self-uri, series, series-text, series-title, sig, size, source, speaker, speech, state, statement, std, std-organization, string-conf, string-date, string-name, styled-content, sub-article, subj-group, subtitle, suffix, supplement, supplementary-material, table-wrap, table-wrap-group, target, term, textual-form, trans-abstract, trans-source, trans-subtitle, trans-title, trans-title-group, unstructured-kwd-group, uri, verse-group, verse-line, version, volume, volume-id, volume-issue-group, volume-series, x, xref, year

Source 

<xs:attribute name="lang">
  <xs:annotation>
    <xs:documentation>
      <div>
        <h3>lang (as an attribute name)</h3>
        <p>denotes an attribute whose value is a language code for the natural language of the content of any element; its value is inherited. This name is reserved by virtue of its definition in the XML specification.</p>
      </div>
      <div>
        <h4>Notes</h4>
        <p>Attempting to install the relevant ISO 2- and 3-letter codes as the enumerated possible values is probably never going to be a realistic possibility.</p>
        <p>See BCP 47 at
          <a href="http://www.rfc-editor.org/rfc/bcp/bcp47.txt">http://www.rfc-editor.org/rfc/bcp/bcp47.txt</a>and the IANA language subtag registry at
          <a href="http://www.iana.org/assignments/language-subtag-registry">http://www.iana.org/assignments/language-subtag-registry</a>for further information.</p>
        <p>The union allows for the 'un-declaration' of xml:lang with the empty string.</p>
      </div>
    </xs:documentation>
  </xs:annotation>
  <xs:simpleType>
    <xs:union memberTypes="xs:language">
      <xs:simpleType>
        <xs:restriction base="xs:string">
          <xs:enumeration value=""/>
        </xs:restriction>
      </xs:simpleType>
    </xs:union>
  </xs:simpleType>
</xs:attribute>

Sample