sections in flexform check access to language 0 even if record is in another language
This problem may be best seen in action with templavoila, but it is caused by the core handling of sections in flexforms.
When a section is defined in a flexform, the function getSingleField_typeFlex_draw in class t3lib_TCEforms checks if the user has access to the default language. This check is even done, when the record is totally unrelated to the default language, e.g. when you have a localized copy of an fce or a flexform in a simple extension record.
When a user has no access to the default language, he can not create a new entry in the section, but only edit the already existing.
The check should be changed if the user can edit the language of the current record, but probably only if the flexform is configured with langDisable = 1
(issue imported from #M15958)
#7 Updated by Andreas Kiessling about 2 years ago
disableChildren and friends has nothing to do with that issue
The access check for lang 0 is still there: https://github.com/TYPO3/TYPO3.CMS/blob/38a1bc5dd7990b63e45c0419065cd02fe91187e9/typo3/sysext/backend/Classes/Form/Container/FlexFormSectionContainer.php#L50
So you can't restructure sections or add new elements without access to language 0. IMHO this is a bug or should be at least configurable.