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 (https://github.com/medzuslovjansky/dictionary-hunspell), 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!