Language Tag

• https://datatracker.ietf.org/doc/html/rfc5646
• ETF language tag
• tag
  • language - shortest ISO 639 code
    • extlang - ISO 639 codes
  • script - ISO 15924 code
  • region
    • ISO 3166-1 code
    • UN M.49 code
  • variant
  • extension
  • privateuse
• Codes for constructed languages