Could you add a few language codes for Slavic auxiliary zonal languages?

First of all, thanks for looking into this!

As a member of Interslavic (constructed language) volunteer programmer team, I’d like to inquire, whether you could assist with adding a few reserved codes for pan-Slavic languages? According to the BCP47 notation, we’d fit best at “sla-Latn”, “sla-Cyrl” language tags (since Interslavic has two alphabets: latin and cyrillic). That would fit the best our current use case, as Interslavic doesn’t have yet an assigned ISO-639-3 code, although it already has received its code on Glottolog (Glottolog 4.4 - Interslavic zonal constructed language).

The context is the following. We’ve got a Hunspell dictionary in works (, and it is quite close to the first beta release, and we’d like to ship also it as a LibreOffice extension. In the worst case, we could have used one of Serbian locales, probably, but it does not feel like the most optimal solution anyway.

What could you advise in our case?
Again, thanks a lot for your time! We’d be happy to hear from you back!

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You can use any syntactically valid (!) BCP 47 language tag as document/paragraph/character attribution language. You can simply enter such tag in the font attribution’s Language combobox, or even better, if you already have a Hunspell dictionary LibreOffice extension that can announce its supported language tag(s) in the dictionaries.xcu Locales property and they will be automatically added to the language list (displayed for example as {sla-Latn} or {sla-Cyrl}). With upcoming version 7.3 even the language/script/country names are displayed along for such a tag, if known.

Btw, Glottolog IDs are not relevant for BCP 47 IANA language tags. If adding your language to ISO 639-3 turns out to be not successful then you might try to register an IANA language variant subtag if you have a very good case.

Also, to prevent future clashes, I recommend to rethink the use of sla-Latn and sla-Cyrl because sla is a generic collective macrolanguage code for Slavic languages. Maybe better suited would be adding a private-use variant subtag, and as you already seem to use x-isv (according to your github page) that would be sla-Latn-x-isv and sla-Cyrl-x-isv. However, the x-isv is a reserved for private use subtag and not interoperable and interpretation in applications depends solely on agreement.