From [https://bitbucket.org/tagoh/liblangtag]. An interface for BCP47 language tags.

Updated IANA Language Subtag Registry files are available as
[https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry]
and per convention are stored as a data/language-subtag-registry file in a
language-subtag-registry-YYYY-MM-DD.tar.bz2 archive, with YYYY-MM-DD being the
File-Date entry of the file, for example
language-subtag-registry-2015-08-04.tar.bz2, and uploaded to the external
sources repository to be included in the build of liblangtag. See download.lst
LANGTAGREG_TARBALL and LANGTAGREG_SHA256SUM.
