LangTags: IANA Language Tags for Elixir

Work with IANA language tags in Elixir, based on BCP 47 (RFC 5646) and the IANA language subtag registry.

The registry is parsed at compile time into pattern-matched function heads, so lookups are plain function dispatch: there is no runtime parsing, no ETS table, no process to supervise, and no runtime dependencies.

Installation

Add lang_tags to your dependencies in mix.exs:

def deps do
  [{:lang_tags, "~> 0.2"}]
end

Usage

Look up a subtag:

iex> LangTags.language("en")
%{"Record" => %{"Added" => "2005-10-16", "Description" => ["English"],
    "Subtag" => "en", "Suppress-Script" => "Latn", "Type" => "language"},
  "Subtag" => "en"}

Resolve a deprecated or grandfathered tag to its preferred value:

iex> LangTags.Tag.preferred("i-klingon")
%{"Tag" => "tlh"}

Format a tag according to the RFC 5646 case conventions:

iex> "az-latn-az" |> LangTags.Tag.new() |> LangTags.Tag.format()
"az-Latn-AZ"

Validate a tag, and find out why it was rejected:

iex> LangTags.Tag.valid?("en-GB")
true

iex> LangTags.Tag.valid?("gsw-Latn")
false

iex> LangTags.Tag.errors("gsw-Latn")
[%{code: :suppress_script, subtag: "latn",
   message: "the script subtag 'latn' is the default for language 'gsw' and should be omitted"}]

errors/1 reports every problem it finds rather than stopping at the first, so a caller can show them together. See the documentation for the full list of codes.

Search tags and subtags by description, with exact matches first:

iex> LangTags.search("Maltese") |> Enum.map(&LangTags.SubTag.format/1)
["mt", "mdl", "mdl"]

Check which types a string is registered as:

iex> LangTags.types("xml")
["extlang", "language"]

Report the date of the bundled registry:

iex> LangTags.date()
"2026-08-08"

See the documentation for the full API.

Updating the registry

The IANA registry changes over time. To refresh the bundled copy:

$ mix lang_tags.update
$ mix compile --force

The recompile is required because the registry is baked in at build time.

Use mix lang_tags.update --check to report whether an update is available without writing anything; it exits non-zero when one is, so it can drive a scheduled job.

Changelog

See CHANGELOG.md.

Javascript version

This project is an Elixir version of the language-tags Javascript project.

License

Apache License 2.0. See LICENSE.

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