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.