TYPO3 Core

Following situation is given:

You have a language overlay of an image-CE. You delete the overlay and for whatever reason the sys_file_reference record pointing to this translated image-CE is not being deleted (I didn't figure it out yet how this happened).

If you then try to localize the image-CE again only the image-CE itself gets localized and you get the error "Localization failed; There already was a localization for this language of the record!" because the sys_file_reference record is still there pointing with its l10n_parent column to the sys_file_reference record which should be localized.
Unfortunately you can't fix this in the BE, because you don't see sys_file_reference records in the BE.

The refindex update and the FAL reindex scheduler task won't help you either.

These inconsistent sys_file_reference records should definitely be garbage collected by the FAL reindex task.