Importing translated content with an image throws error if the translation doesn't exist

Problem/Motivation

In a multilingual site, when exporting content with an image and translations checked, importing that content when the translations are deleted gives an error "Invalid translation language (und) specified."
This does not occur when the content still has the translated version (e.g. the content and its translations still exist and are updated), or if the content does not have images.

Steps to reproduce

• Create a multilingual site
• Create content in multiple languages (e.g. Default and Dutch) with an image
• Export the content with include translations checked
• Delete the translation
• Try to import the content