Give more information when import doesn't work

Hello,

I'm currently trying to deploy some pages with files/media/paragraphs in it, in 4 languages.
This quickly leads to dozens of json files.

When trying to import through drush, I'm getting Invalid translation language (und) specified. error (In ContentEntityBase.php line 956).

But I don't know on which specific file it stops, if we could have at least the file being imported we could try to fix it.

Thank you!