Smart locale fallback

[Malte Beckmann]

We got a standard locale fallback to "en" if the browser language is not supported by our site. 

However, it would make sense to fallback from en_AU to en_UK rather than to en which is essentially en_US. Or zh_hans to zh_CN which are essentially the same.

I am sure this can be done but I doubt I am the first person to think this should happen this way. Has anyone tried this before? Cheers/malte