Improve preferred and default language

[JayPanoz]

Handling of preferredLanguages is not smart enough when sorting as it will not detect language and language-region in the array, and sanitise/normalise it.

In addition JSON data’s defaultRegion is not being used as a fallback when sorting language.

[HadrienGardeur]

In a way, I think that we should almost keep language and region preferences partially separate from one another.

I'll focus specifically on regions in this comment. We need a heuristic that can be reasonable implemented, here's a proposal:

• first of all, when inferring regional preference, we need to get rid of BCP-47 language tags with only two letter codes (countries), they're not helpful
• it's also technically possible to provide multiple regional preferences for a single language, we need to keep that in mind and be capable of ranking them
• when sorting regional preferences, we should look for a full match first (for example if my browser returns fr-FR in navigator.languages() then "France" should be my preferred region for French)
• if we can't have an exact match, we should also consider regional preferences from other languages (for example if my browser returns en-CA but nothing for French, then we should consider ca for French as well and use fr-ca)
• and finally, if we can't infer any regional preference, we should fallback to a default region per language, as documented in the JSON files for voices contained in this repo