TYPO3 Core

There's currently a bug in DataHandler that creates a broken localization state, which in turn breaks the FormEngine frontend.

This can be reproduced in the following way:

1. Create a new page and define the "Author Email" (to be found in the "Metadata" tab)
2. Create a localization of the created page
3. Update the localization, change the translation behavior of the "Author Email" field to "Custom value" and insert a custom value -> save
4. Copy the whole page
5. Edit the localization of the copied page

The underlying issue is caused by DataHandler since at least v11. In v12, jQuery is not used anymore in the offending part, revealing this issue.