[feat] Allow adding new locales to the list of valid locales

[nemphys]

Describe the feature

Right now, trying to use any locale that is not in the (hard-coded) list from ladjs/i18n-locales throws an error.
When this is required, there in no other option but to patch the module.

Checklist

• [ X ] I have searched through GitHub issues for similar issues.
• [ X ] I have completely read through the README and documentation.

[titanism]

PR welcome