That’s a good point, just making a mental note that the default language attribute is normally indicated in the top-most html tag, so that it’s inherited by all elements, unless otherwise specified:
<html lang="en-US">
<head>
<title>...</title>
<body>
<h2>Abstract</h2>
<p>My abstract in English.</p>
<div lang="es-ES">
<h2>Abstracto</h2>
<p>Mi resumen en español.</p>
</div>
Another issue is metadata, I noticed that Luca managed to include both primary and secondary languages:
<meta name="DC.Language" scheme="ISO639-1" content="it"/>
<meta name="DC.Title" content=" Intervista con Catherine D’Ignazio: Data Feminism nella storia urbana e nel patrimonio"/>
<meta name="DC.Title.Alternative" xml:lang="en" content=" Interview with Catherine D’Ignazio: Data Feminism for Cultural Heritage and Urban History"/>
My understanding is that, although Google Scholar specificially doesn’t support multilingual metadata in their own citation tags (see here), the more general Google Search would take in multilingual Dublin Core tags.
-Felipe.