What does being valid really mean?
<外语 й="ڰ" lang="uk">Китайська мова - Ukrainian for the term 'Chinese language' within a<外语> element.
<外语 й="ڰ" lang="uk">Китайська мова - <span lang="en">Ukrainian for the term 'Chinese language' within a <span><code><外语></code></span> element</span>.</外语><החוץ> element.
<החוץ й="स्पेनिश" lang="es">Lengua Alemana - <span lang="en">Spanish for the term 'German language' within a <span dir="rtl"><code><החוץ></code></span> element</span>.</החוץ>Other test with Unicode can be found here