Hi again, I found a workaround, too simple and too dirty to trust it but i'll explain it here.
Before going on let me say that I asked my provider (shellrent.com, or their office in Italy) about the support of en_US but their answer was really evasive: "the locale is on, at least you can use it in Italian" :(
While I was waiting for a new answer to a more specific question about the same problem, I made this simple experiment:
1) I deleted the locale folder de_DE. I don't need it atm and German locale was working on my server.
2) I renamed the folder en_US to de_De
3) In functions-i18n.php I replaced the string:
`'de_DE' => gettext('German (Germany)'),`
With:
`'de_DE' => gettext('English (United States)'),`
I know it's crazy but everyting works as needed now.
Feel free to remove this post if it can lead to improper use of your CMS by other people. This is non compatible with whatever upgrade of course.
ciao
bic
edit:
Of course the AcceptLanguage doesn't work in this way