Return the BCP-47 locale code for a given ISO 639-1 language code. Falls back to en_GB for unknown languages — the same fallback the rest of the site uses for missing translations.
en_GB
ISO 639-1 language code (e.g., "en", "sv")
"en"
"sv"
BCP-47 language_TERRITORY locale (e.g., "en_GB")
language_TERRITORY
"en_GB"
Return the BCP-47 locale code for a given ISO 639-1 language code. Falls back to
en_GBfor unknown languages — the same fallback the rest of the site uses for missing translations.