aakk9999 - 5:54 pm on Nov 5, 2012 (gmt 0)
I am sorry, I did not want to upset you and I think you perhaps misunderstood what I said.
I was not saying that Google should go back and use lang="en" either.
What I was saying is that whilst Google does not use HTML language attributes, it does not always go by the language it sees on the page either - which seems to more impact sites in english hosted in non-english country and being owned by local company.
It appears that whilst Google initially gets language correct (just as you said, recognising language the page is written in), it must be also folding in some local signals which with the time tip over Google's understanding of the language (local traffic with browser language set to local language, perhaps?).
So at some point Google suddenly decides the language the page is written is not English - but on the other had, cutting/pasting the whole text from the page into Google Translate makes Google recognise language correctly as English.