This has been the case for a while (at least since 5.8?). The language code in the user agent string (and possibly elsewhere in the HTTP headers) is always 'en-US' on my machines, despite my preferred language in System Preferences being set to Australian English. Safari, on the other hand, uses 'en-au'.
This is despite having 'Request web pages in my preferred language' turned on OmniWeb's preferences.
David
This is despite having 'Request web pages in my preferred language' turned on OmniWeb's preferences.
David