I have a website with Polylang and Metabox. I need to manage the alt tag for every languages so I enabled the image duplication in the Polylang settings.
When I open the media selector popup it doesn't show the corresponding translated image.
Here a video to better explain my issue.
I think the issue is not related to Meta Box, it just helps you to select the image in the media popup. You can try again with the option Featured Image of WordPress to re-check it.
It is possible that the version of Polylang on your site does not support translating the media, you can follow this documentation to use Polylang Pro to translate the media https://polylang.pro/doc/working-with-media/