ext_localconf.php

<?php

if (!defined('TYPO3')) {
    die('Access denied.');
}

//Register cache
if (!isset($GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tx_bgmhreflang_cache']) || !is_array($GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tx_bgmhreflang_cache'])) {
    $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tx_bgmhreflang_cache'] = [];
}

//Clear cache whene page cache is cleared
if (!isset($GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tx_bgmhreflang_cache']['groups'])) {
    $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tx_bgmhreflang_cache']['groups'] = ['pages'];
}

$GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['nodeRegistry'][1603836773] = [
    'nodeName' => 'bgmhreflangList',
    'priority' => 40,
    'class' => \BGM\BgmHreflang\Form\Element\HreflangTagsElement::class,
];

//Register old and new related pages for cache clearing after changes in the backend
$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['t3lib/class.t3lib_tcemain.php']['processDatamapClass'][] = \BGM\BgmHreflang\Hooks\DataHandler::class;

//Cache is cleared in frontend for all related pages if no cache entry for the current page has been found.
//Here you can disable this behaviour, if you are sure the new DataHandler backend hook is enough cache clearing.
$GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['bgm_hreflang']['feature']['clearCacheInFrontent'] = true;

/**
 * DEMO CONFIGURATION
 */
/*
//"sys_language_uid" and "isolanguagecode" have to be unique in the array $languageMapping!
$languageMapping = array(
    //sys_language_uid => isolanguagecode,
    1 => 'de', //Deutsch
    2 => 'en', //Englisch
    3 => 'fr', //Französisch
);
//"pageid" is the rootpage of a country tree. It has to be unique in the array $countryMapping!
//"isocountrycode" has to be unique in the array $countryMapping!
$GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['bgm_hreflang']['countryMapping'] = array(
    pageid => array(
        'countryCode' => isocountrycode,
        //"$languageMapping + array(0 => isolanguagecode)" can be assigned more than once with the same isolanguagecode as languageMapping in the array countryMapping.
        'languageMapping' => $languageMapping + array(0 => isolanguagecode),
        //"additionalGetParameters" is optional
        'additionalGetParameters' => array(
            //"sys_language_uid" has to be unique in the array $additionalGetParameters!
            sys_language_uid => isolanguagecode,
        ),
        //domainName is optional
        'domainName' => 'https://www.domain.tld',
        //"additionalCountries" is optional
        'additionalCountries' => array(isocountrycode2, isocountrycode3),
    ),

    12 => array( //International
        'countryCode' => 'en',
        'languageMapping' => $languageMapping + array(0 => 'en'),
        'additionalGetParameters' => array(
            1 => '&foo=bar',
        ),
        'domainName' => 'https://www.my-domain.com',
    ),
    34 => array( //Deutschland
        'countryCode' => 'de',
        'languageMapping' => $languageMapping + array(0 => 'de'),
        'additionalCountries' => array('at', 'ch'),
        'domainName' => 'https://www.my-domain.de',
    ),
    56 => array( //UK
        'countryCode' => 'gb',
        'languageMapping' => $languageMapping + array(0 => 'en'),
        'domainName' => 'https://www.my-domain.co.uk',
    ),
    78 => array( //France
        'countryCode' => 'fr',
        'languageMapping' => $languageMapping + array(0 => 'fr'),
    ),
);
//If L==0, pages in this tree are rendered with 'x-default', else only the isolanguagecode is used (without the isocountrycode)
$GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['bgm_hreflang']['defaultCountryId'] = 12;
*/