Feature/dev 1088 custom locale aliases

[brandonkelly]

Description

Adds support for custom locale aliases, via a new localeAliases config setting.

Locale aliases can be selected alongside ICU-defined locales in users’ “Formatting Locale” settings and sites’ “Language” settings.

Example locale alias definition:

// config/general.php
return GeneralConfig::create()
    ->localeAliases([
        'smj' => [
            'aliasOf' => 'sv',
            'displayName' => 'Lule Sámi',
        ],
    ]);

A side effect of this change is that there could now be locale IDs floating around that aren’t actually understood by the Intl extension, which could cause errors. So plugins and modules should be careful to always instantiate craft\i18n\Locale objects via craft\i18n\I18N::getLocaleById($id) rather than new Locale($id).

Related issues

• [4.x] Add Lule Sami language code for sites #12703

[linear]

DEV-1088 Custom locale aliases

It should be possible to define aliases of existing locales, with custom locale IDs and display names.