Firefox on Android doesn't use valid BCP 47 language tags

[HadrienGardeur]

As identified while documenting voices, Firefox on Android doesn't return valid BCP-47 language tags, instead it returns:

• a lowercase three letter code (eng) for languages, instead of a two letter code (en)
• followed by an uppercase two letter code for the region (US) as it should be
• and some random string with a lowercase three letter code (f000)

Links:

• TBD