The ISO 639 code that I know for Esperanto is eo. As far as I know, and according to RFC 3066 there are no recognized distinct variant.

For example French have many variants: fr-AD, fr-BE, fr-BF, fr-BI, fr-BJ, fr-CA, fr-CD, fr-CF, fr-CG, fr-CH, fr-CI, fr-CM, fr-DJ, fr-FR, fr-GA, fr-GB, fr-GF, fr-GN, fr-GP, fr-HT, fr-IT, fr-KM, fr-LB, fr-LU, fr-MC, fr-MG, fr-ML, fr-MQ, fr-NC, fr-NE, fr-PF, fr-PM, fr-RE, fr-RW, fr-SC, fr-TD, fr-TG, fr-VU, fr-WF, fr-YT.

So can I indeed conclude that there is no official eo-.. code out there?

  • 1
    As there are no distinct variants of Esperanto I would assume that you are correct in concluding that there are no distinct ISO code variants either. Commented Jan 27, 2017 at 15:54
  • There are ways of making the Esperanto characters. Kern punkto has an interesting discussion of it here: kern.punkto.info/2016/11/24/kp100-unikodo . In Esperanto, klare...
    – Karlomanio
    Commented Jan 27, 2017 at 17:07

1 Answer 1


IETF RFC 3066 is obsolete. The current authoritative reference for language tags is IETF BCP 47: Tags for Identifying Languages. The document by Tex Texin and John Cowan that you reference is explicitly marked as a draft and was last updated in January 2005, four years before the publication of IETF BCP 47.

IETF BCP 47 does not list the accepted ISO language tags but defines how to use language tags, e.g. the choice between an ISO 639-1 two-letter code and an ISO-639-3 three-letter code, and how to add country codes and/or script codes.

The list of ISO 639-1 language codes is maintained by Infoterm in Austria, list of ISO 639-3 language tags is maintained by SIL, while the list of ISO 3166 country codes is maintained by the ISO 3166 Maintenance Agency in Geneva.

IANA maintains a subtag registry (defining, e.g. eo-Latn as the only Esperanto-related tag), but it is not clear who or what would give IANA the authority to prohibit tags that are not in their registry.

As far as I can see, you can, strictly speaking, create codes such as eo-FR, assuming that there is (in this case) a specific French variant of Esperanto, but what would be the use case for such a tag and which tools would support it?

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