The fallback language taken from the site confguration in a single tree setup is saved in a different way in JCR compared to the other available languages.

Translated items in the fallback language are stored without underscore while other languages have one:

This leads to all kinds of problems:

• if the default / fallback language is ever changed, saved data in the tree are not adjusted so it moves into an inconsitent state
• the content translation tool fails because it shows text in the wrong column
• you possibly cannot reuse translated nodes in other trees depending on the language configuration for the tree