In HTML5, the "language" attribute for script is claimed obsolete:
http://www.w3.org/TR/html-markup/script.html[
^].
However, nor attribute, neither "lang" weren't really needed earlier. Please see what HTML 4.01 specification says:
http://www.w3.org/TR/html401/interact/scripts.html#h-18.2.2[
^].
Script element language is controlled by the attribute "content".
However, perhaps there is a confusion. What do you mean by "language"? Computer language or the language associated with the human cultures (English, French, etc.)? If you mean the second thing, I don't see why such attribute should belong to the scrip. Script is code, should be neutral. If you used some culture-specific text in the code of script, it would be a bad practice; you could always get some text you need from data, such as HTML DOM itself.
—SA