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Never seen it done before. Obviously no use for a country-specific site, but do you think it's worth doing that for international sites? Or is it a waste of time?
If you are doing different languages you should probably be doing different pages, or even different sites. Whether or not you do all the meta tags for those pages is up to you, but if I did I probably would do them in the appropriate language format.
W3C - 7.4.4.2 - The META Element [w3.org]
Be sure to read the whole section as you will find exactly what you are looking for there.
Then after that, wrap it up by reading here...
W3C - Notes on helping search engines index your site [w3.org].
Read carefully as the information is of great importance. There is much that can be done when dealing with translated content.