There's a potentially tricky terminology problem. People who care about processing multilingual text (which is a lot of people, these days) generally refer to the process of identifying a text's language as "language tagging". This is pretty obvious, but there's a problem, because in XML terms, xml:lang isn't a tag, it's an attribute, which can be attached to any old XML tag.
So to summarize, you can language-tag tags, but the tags you tag the tags with are attributes, not tags. So to speak.
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