Adding language metadata on code elements

The current draft states:

“Although there is no formal way to indicate the language of computer code being marked up, authors who wish to mark code (http://www.w3.org/TR/2011/WD-html5-20110525/text-level-semantics.html#the-code-element) elements with the language used, e.g. so that syntax highlighting scripts can use the right rules, may do so by adding a class prefixed with "language-" to the element.”

I was wondering why this is the preferred way over a data attribute such as "data-langauge"? Is this bug-worthy or is there already a discussion in the archive that I overlooked?

-Kevin