phranque - 4:08 pm on Oct 22, 2012 (gmt 0)

even though support of it maybe be limited to Google* it's not a proprietary attribute

thanks for pointing that out - i was inaccurate in that characterization.

for those interested, here's the W3C reference specific to that link element implementation.
Links and search engines:
http://www.w3.org/TR/html401/struct/links.html#h-12.3.3

Do they also ignore the content-language http header?

they did not mention header-level language specification, only code-level Language information:
http://www.w3.org/TR/html401/struct/dirlang.html [w3.org]

this means the discussion really only applies to the lang attribute.

even the "link rel alternate hreflang" element can also have its own lang attribute to specify the language of its title attribute, for example.
ironic that google would ignore that lang attribute here while being attentive to the hreflang attribute.


these all have different meanings.
for example, the HTTP Content-Language header can have multiple language values specified.