weird behaviour of automatic language selection

[Federico Bruni]

Hi all

I'm testing the lilypond website on the web root of my local Apache 
installation.
I've noticed that _on the same browser_ I get different languages on my 
localhost:

http://lilypond.org/manuals (italian, correct) - all the other URLs 
serve correctly italian pages

http://localhost/manuals (nederland, incorrect) - some other pages are 
served in english (e.g. download/ and introduction/), but others are 
served again in nederland (e.g. features/)

Strange indeed.
Do you have any idea of why it happens? Perhaps I miss some 
configuration on my Apache installation?

Before studying Apache content negotiation, let's see if I can get some 
help quickly :)

Thanks in advance
Federico