Most meta tags are completely useless:
- keywords is not used in ranking by Google and has almost no value (if not zero value) in other search engines.
- description is used by search engines but because SO's content is entirely user-generated it's impossible to include a relevant meta-description that doesn't just repeat what's already on the page.
- robots should be replaced by the more reliable robots.txt.
- language is pretty much ignored by search engines. Regardless, the correct way to specify language is to use the
lang
attribute.
All the other tags are pretty much fluff that should either be set with HTTP headers (e.g. expires), visible on the page itself (e.g. copyright, author), or removed entirely (e.g. generator).