Doing it on browser language is easy to search google for, (and indeed can be done in apache).
Doing it on IP, you need IP->country data.
www.ip-sorter.com is our implementation of the maxmind.com data, 100% C based system that can redirect or transparently display content to international surfers, using their ip or/and language.
$200 when using the free data, $300 when using the premium data.
Cheap when compared to people asking $1000s/month, expensive when compared to free, but always easy to use
