I've updated the patch for Drupal 10.3.1
I've created a (temporary) patch that fixes the issues mentioned in my previous comment and adds default behavior to use the current site language as the render language when the langcode field is not explicitly set.
I've noticed that the build path for the index.js file is not correct, there is a '/' missing in the Telephone.php file (line 129).
It would also be beneficial, as we are trying to translate countries for accessability reasons, to always translate them to the current language of the page (especially when a language switch is available).
This could also be a checkbox 'use site default language' and hide the field for the langcode when checked.
I hope this is helpful feedback.
~ Josh
Providing patch resolving issue with the form display setting
Providing patch that resolves this issue