This header includes a pair of two-character identifiers separated by a hyphen character. This language code indicates the browser's default language setting. This method relies on the browserLanguage property of the navigator object . Users can change their browser's default settings starting with both Internet Explorer 4.0 and Navigator 4.0. That means that users can change their default language after they have visited your site, so don't cache it in a user profile.
Most U.S.-manufactured computers ship with English as the default browser setting.
Finally, most users don't know how to change their default language setting later. So when you see an English-language browser, that doesn't always mean the customer prefers English. Also, each language version uses its own domain so customers can manually choose the language version they prefer. Many of you are looking for definitive ways to handle broader browser-locale issues, such as local currency, time zone, and other information needed to created a truly international site. This is a huge topic that I won't even attempt to address here.