Language Tags (BCP 47)

1. Syntax of language tags

   Language, script, region, variant and extension subtags.

2. Language subtag sources

   ISO 639, ISO 15924, ISO 3166-1 and UN M.49 subtags.

3. Choice of language tag

   Guidelines for tagging content.

4. Primary language subtag

   ISO 639 language codes such as en, zh and fil.

5. Canonicalization of language tags

   Canonical form and case conventions.

6. Extended filtering of language tags

   Basic and extended filtering of language ranges.

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