Feature request : web feed : support language

[pinage404]

Hello,

The documentation doesn't mention language https://fed.brid.gy/docs (there is one mention but unrelated)

I would like support of xml:lang with Atom feed
https://en.wikipedia.org/wiki/Atom_(web_standard)#Internationalization

Related to #1134 (comment)

[snarfed]

Thanks for filing! This should be a pretty simple place to get started with if you're interested in contributing. It would go into granary/atom.py, maybe using this feedparser attr: https://feedparser.readthedocs.io/en/latest/reference-entry-content/#entries-i-content-j-language .