TYPO3 Core

I made some tests with a fresh Typo3 8.7.20 instance and can confirm the above issue.

TCA for `pages`:

$tca = [

    'tx_apxsample_category' => [
        'exclude' => 1,
        'label'   => 'Category',
        'config'  => [
            'type'          => 'select',
            'renderType'     => 'selectSingle',
            'size'          => '1',
            'itemsProcFunc' => "Vendor\\Apxsample\\Lists\\Categories->tcaCategories",
        ]
    ],

    'tx_apxsample_category2' => [
        'exclude' => 1,
        'label'   => 'Category',
        'config'  => [
            'type'          => 'select',
            'renderType'     => 'selectSingle',
            'size'          => '1',
            'items' => [
                ['Category A', 0 ],
                ['Category B', 1 ],
                ['Category C', 2 ],
                ['Category D', 3 ]
            ],
        ]
    ],

];

TCA for `pages_language_overlay`:

$tca = [

    'tx_apxsample_category' => [
        'exclude' => 1,
        'label'   => 'Category',
        'config'  => [
            'type'          => 'select',
            'renderType'     => 'selectSingle',
            'size'          => '1',
            'itemsProcFunc' => "Vendor\\Apxsample\\Lists\\Categories->tcaCategories",
            'behaviour' => [
                    'allowLanguageSynchronization' => 1
            ]
        ]
    ],

    'tx_apxsample_category2' => [
        'exclude' => 1,
        'label'   => 'Category',
        'config'  => [
            'type'          => 'select',
            'renderType'     => 'selectSingle',
            'size'          => '1',
            'items' => [
                ['Category A', 0 ],
                ['Category B', 1 ],
                ['Category C', 2 ],
                ['Category D', 3 ]
            ],
            'behaviour' => [
                'allowLanguageSynchronization' => 1
            ]
        ]
    ],

];

Here's the list used by itemsProcFunc:

    static public function tcaCategories($config){

        $config['items'] = [
            ['Category A', 0 ],
            ['Category B', 1 ],
            ['Category C', 2 ],
            ['Category D', 3 ]
        ];

        return $config;
    }

Result of a translated page (see attached image)

`BackendUtility::getLabelsFromItemsList` does not support `itemsProcFunc` and it produces a display bug on `otherLanguageContent` field when working with a `select`.

The code that should return the label, only checks for `items` and does not try to process that `itemsProcFunc`: https://github.com/TYPO3/TYPO3.CMS/blob/master/typo3/sysext/backend/Classes/Utility/BackendUtility.php#L1732

`BackendUtility::getLabelsFromItemsList` should also check if `itemsProcFunc` is in the config and call `GeneralUtility::callUserFunction` in that case. (I understand that some changes to callUserFunction could be needed, specially for the $ref part)

In the PHPDoc, there's `NOTE: this does not take itemsProcFunc into account`, but there's nothing about that in the documentation.

Patch set 1 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/59156