feat(ios): dynamic locale selection, support

**Is your feature request related to a problem? Please describe.**
Right now, our current design for iOS localization is quite tied to the Apple system menu's setting. If iOS doesn't officially support a language in any manner, the app simply can't support that language.

However... there are a few leads I've found that may make it possible, while not deviating _too far_ from our currently-established i18n infrastructure:

**Describe the solution you'd like**

Those leads indicate a way we could support an in-app selector for a user's preferred language.

https://www.google.com/url?q=https://stackoverflow.com/questions/29985614/how-can-i-change-locale-programmatically-with-swift&sa=D&source=editors&ust=1614910240172000&usg=AOvVaw2YlARgx2sOJBYf4pDRUQIg

https://www.google.com/url?q=https://www.factorialcomplexity.com/blog/how-to-change-localization-internally-in-your-ios-application&sa=D&source=editors&ust=1614910240173000&usg=AOvVaw0tXRTnizAhlx16EiPDweMj

This would likely make i18n coding more complex, due to the requirements to manually select appropriate bundles - and that, for both the engine and app. Getting that right and making it 'simple' / maintainable would likely take some effort.

... but, this should let us support arbitrary language codes for l10n, so if/when we want to push for that, it does look possible.