This rules are for display the target language of a link when it is different of the text who contain it. It include a lot of scenario, according different attributes.
Because the "lang" attribute isn't always informed, I write too Always display target link language , who always display hreflang (when the lang attribute is not specified).
For example :
- when the text is english, and the target on french => (fr)
- when the text is english, and the text of the link and the target are in french => (fr)
- when the text is englsih, and the text of the- link is french and the target is german => (de)

This rules take in charge all target language, but to add a redaction language, just add declaration with the language name.
Because the language can be specified with an attribute Regional (e.g. "en-us"), I use CSS3 selector who allow to specify "who start by" : ^. So it can make problems on browser who don't support CSS3 (but yes, firefox 3.* support CSS3)

For more explications, look at http://delavy.h