RFC 4646 is a document that defines a standard for language tags used in computer systems. It specifies how to represent languages, regions, and scripts in a consistent format, allowing software to identify and process different languages effectively. This standard is essential for applications that need to support multiple languages, such as web browsers and content management systems. The document builds on earlier standards, particularly RFC 3066, and introduces a more structured approach to language tagging. It allows for the inclusion of subtags, which can specify dialects or variations, enhancing the accuracy of language representation in digital communication.