Language identifiers and details: Support more than one language per ISO 639-3 code

[markboots]

The first draft of Flow Spec used bare ISO 639-3 codes to identify languages. This was assumed possible since ISO 639-3 is supposed to contain every human written and spoken language.

However, what the consortium realized in discussions over time is that 639-3 alone doesn't make sense as a "primary key" for languages in flows, because:

• It could be common to have multiple "languages" with the same 639-3 code, to support use-cases where organizations might have distinct sets of content ("language variants") for the same 639-3 value. A common example of variants could be "English - India" and "English - East Africa", or "English - Male voice" and "English - Female voice".
• There might be rare cases of languages with no 639-3 code.

There is also additional data that might be useful to associate with languages, beyond the ISO 639-3 code; an example is the BCP 47 language+locale, useful often in conjunction with speech recognition and synthesis tools, etc.

Possible solution:

languages: [
   {
      id: "eng-male",
      label: "English - Male Voice",
      iso_639_3: "eng",
      variant: "male",
      bcp_47: "en-US"
   },
   {
      id: "eng-female",
      label: "English - Female Voice",
      iso_639_3: "eng",
      variant: "female",
      bcp_47: "en-US"
   },
   {
      id: "mis-mysecretlanguage",
      label: "My secret code language",
      iso_639_3: "mis",
      variant: "mysecretlanguage",
      bcp_47: null
   },
   {
      id: "fre",
      label: "Francais",
      iso_639_3: "fre",
      variant: null,
      bcp_47: fr-FR
   }
]

The language id would be a string, but the recommended format for language IDs would be:

• -variant, where the variant is not null.
• , when the variant is null.