A locale 1) refers to a national language and the region in which the language is spoken.
Generally a locale identifier consists of at least:
Any special variant preferences can be added.
en-US
It will be used by application to choose the character set used to encode string.
Render or parse data type with the appropriate locale formatting, such as using the correct:
The locale is the key parameter that permits to localize an application .
Search Engine are also using this information set in web meta to localize the content.
See the Unicode Common Locale Data Repository. For instance, for the data: http://www.unicode.org/Public/cldr/27.0.1/
You can find the Language Tags and Locale Identifiers for the World Wide Web on this page.