lang:en - Are you blogging in multiple languages?

Today I was told that there might be some kind of ’standard’ to tag entries with different tags depending on the choosen language for the post. The tag should be lang: followed by the two character ISO language code. For example lang:en. Searching forlang:en gives 360.000 hits. But I can’t find any defined or even de-facto standards.

If you know anything about this, especially how to take advantage of this when creating the feeds. It would be practial to only deliver english posts to feedburner for example.