So you have a page with content (in the
body) in one language, and you want to provide the metadata (in the
head) in multiple languages.
In general this is easily possible by providing corresponding
lang attributes (see an example with multiple
keywords in different languages), but it doesn’t work in two cases:
Everything else that could be interesting for translation is allowed, I think.
Doing it for SEO purposes probably doesn’t make much sense, as search engine likely have no interest in showing metadata in one language if the content is in another language.
(Also note that most metadata is ignored by search engines in the first place, for example
It shouldn’t harm SEO as long as you don’t deceive with the translations, and as long as you use the
lang attribute to convey in which language the metadata is.
However, it could be problematic for search engines that don’t notice the
lang value difference (they might end up using metadata in the wrong language), but I don’t know of any.
¹ I proposed to allow multiple
description elements if they have different
lang values, but it hasn’t been decided yet.