How to add a custom language in Craft 4

Question

Context

I am now working on a trilingual website in Craft CMS. It needs to be available in french, english and inuktikut (a native american language).

Obviously french and english is easy as 123 but inuktikut is not natively supported in Craft 4 and I can't seem to find a way to add it.

What I have tried

I have come across a bunch of solutions for Craft 2 or 3 before PHP Intl was integrated but I can't seem to find anything in the documentation or anywhere else actually about adding a custom language or locale for use in a Craft site.

I have tried adding a config/locales/iu-CA.php file but it had no effect.

I have also tried adding a custom value to the internationalisation component in config/app.php like so:

'components' => [
   'i18n' => [
      'translations' => [
         'custom' => [
            'class' => \craft\config\CustomMessageSource::class,
            'sourceLanguage' => 'iu-CA',
            'basePath' => '@app/translations/iu',
            'fileMap' => [
               'site' => 'site.php',
            ],
         ],
      ],
   ],
],

Is there a way to add a new language/locale to the sites' language dropdown or any other method to translate a specific site in a custom language?