localizationStateSelector 

The localization state selector wizard displays two or three radio buttons in localized records saying: "This field has an own value distinct from my default language or source record", "This field has the same value as the default language record" or "This field has the same value as my source record". This wizard is especially useful for the tt_content table. It will only render, if:

• The record is a localized record (not default language)
• The record is in "translated" (connected), but not in "copy" (free) mode
• The table is localization aware using the ['ctrl'] properties languageField, transOrigPointerField. If the optional property translationSource is also set, and if the record is a translation from another localized record, the third radio appears.
• The property ['config']['behaviour']['allowLanguageSynchronization'] is set to true

<?php

use TYPO3\CMS\Core\Utility\ExtensionManagementUtility;

defined('TYPO3') or die();

ExtensionManagementUtility::addTCAcolumns('tx_myextension_conference', [
  'contact_email' => [
    'label' => 'my_extension.db:conference.contact_email',
    'config' => [
      'type' => 'email',
      'placeholder' => 'info@example.org',
      'behaviour' => [
        'allowLanguageSynchronization' => true,
      ],
    ],
  ],
]);
ExtensionManagementUtility::addToAllTCAtypes(
  'tx_myextension_conference',
  'contact_email',
  '',
  'before:--div--;core.form.tabs:categories',
);