Metatags in different languages?

We have a number of websites with a global reach. I was having a look at the source code of http://www.germanwings.com and noticed that the metatag descriptions are in different languages. e.g.:

meta name="keywords" lang="de" content="

meta name="description" lang="en" content="

meta name="keywords" lang="fr" content="

Never seen it done before. Obviously no use for a UK-specific site, but do you think it's worth doing that for international sites? Or is it a waste of time?

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