2.1.15 [CSS-Level2-2009] Section 5.11.4, The language pseudo-class: :lang
The specification states:
The pseudo-class ':lang(C)' matches if the element is in language C. Whether there is a match is based solely on the identifier C being either equal to, or a hyphen- separated substring of, the element's language value, in the same way as if performed by the '|=' operator. The matching of C against the element's language value is performed case-insensitively for characters within the ASCII range. The identifier C does not have to be a valid language name. C must not be empty.
Quirks Mode and IE7 Mode (All Versions)
The pseudo-class :lang is not supported.