Always set the language attribute on a WordPress site

[MarcoZ]

On a standard WordPress installation that is not localized (e.g. $WPLANG is empty in wp-config.php), WordPress does not set a default lang and xml:lang attribute on the pages when it renders them. I come from Germany, and while my speech synthesizer used to read text to me is capable of speaking English, it does not switch to it automatically when I load my own or many other WordPress sites. If this lang attribute was set to en-us when there's no override, this would allow the speech synthesizer to switch automatically.

[MarcoZ]

In get_bloginfo, apply the same rule as used in many places in l10n.php. If get_locale returns an empty string, assume en_US (the blog hasn't been localized from its default English language).

[Viper007Bond]

Setting to 2.6. It'll be backported to 2.5.x if need be. :)

[westi]

This looks like a really good idea.

In face I think we should just make get_locale return en_US instead of '' that way we have less code :-)

[westi]

(In [7885]) Always set the locale to something. Fixes #6872 props MarcoZ.