Is multiple description meta tags valid?
Is it valid to define multiple meta description with different languages? Is this valid?
<meta name="Description" lang="en_US" content="Something in here" /> <meta name="Description" lang="pt-BR" content="Algo aqui" /> <meta name="Description" lang="fo-BA" content="Foo bar" />
It's not a good practice. Most probably the search engines will ignore them or even penalize you for spam.
Anyway, why would you have multiple description meta on the same page? I don't really think that your page will be in 3 languages at the same time.
I suppose you will have some language selection function or automatic selection based on user's browser language settings. Then you should output the appropriate description based on the selected language.
Valid, yes. Handled correctly by search engines? Currently it does not appear that they are. Most SEO validators will complain about multiple descriptions even when they are tagged with different language codes and as stated earlier, penalise as spam in some cases.
No reason at all why you wouldn't have a page appearing in multiple languages if it were, for example, discussing the finer points of two, or more, language themselves, being viewed/shared by students of both/all languages, where discussions could happily switch between the various languages during the course of a single thread to make a particular point, say.
I also see no reason why you should not have a page with tags/elements in multiple language, hidden, or shown according to some current context.
We are still in Web 0.9 where people think that because you live in a particular country, your language must be the one associated with that same country, or vice-versa with respect to language, or indeed that one country speaks only one language, e.g. Spain where Euskadi (Basque), Catalan, Galician, Castillian and more are spoken, or Switzerland (German, French, Italian, or Romansh). Poor assumptions to make.
Valid? Yes. There are no real restrictions on what you can have in the way of meta data.
The problem with not having a clear spec is that different consumers will consume them in different ways.