TYPO3 RealURL: Two sites in an installation, both with one domain per language

realurl_conf.php

<?php
$realUrlSiteConfigurations = [
    'site1' => [
        'rootPageUid' => 1,
        'schema' => 'https',
        'languageDomainMap' => [
            0 => 'www.site1.ch',
            1 => 'www.site1.fr',
            2 => 'www.site1.it',
        ]
    ],
    'site2' => [
        'rootPageUid' => 2,
        'schema' => 'https',
        'languageDomainMap' => [
            0 => 'www.site2.ch',
            1 => 'www.site2.fr',
            2 => 'www.site3.it',
        ]
    ]
];

# Could be used to override depending on global configuration, e.g. for staging/latest environment
#$realUrlSiteConfigurationOverrides = require_once(dirname(__FILE__) . '/../../Configuration/current/RealUrlConfiguration.php');
#\TYPO3\CMS\Core\Utility\ArrayUtility::mergeRecursiveWithOverrule($realUrlSiteConfigurations,
#    $realUrlSiteConfigurationOverrides);

$realUrlDefaultConfiguration = [
    'init' => [
        'enableCHashCache' => 1,
        'appendMissingSlash' => 'ifNotFile',
        'enableUrlDecodeCache' => 1,
        'enableUrlEncodeCache' => 1,
    ],
    'redirects_regex' => [],
    'preVars' => [
        [
            'GETvar' => 'no_cache',
            'valueMap' => [
            ],
            'noMatch' => 'bypass',
        ],
        [
            'GETvar' => 'L',
            'valueMap' => [
                'de' => '0',
                'fr' => '1',
                'it' => '2',
            ],
            'noMatch' => 'bypass',
        ],
    ],
    'pagePath' => [
        'type' => 'user',
        'userFunc' => 'EXT:realurl/class.tx_realurl_advanced.php:&tx_realurl_advanced->main',
        'spaceCharacter' => '-',
        'languageGetVar' => 'L',
        'expireDays' => 7,
        'rootpage_id' => 1,
    ],
    'fixedPostVars' => [],
    'postVarSets' => [],
    'fileName' => [],
];

foreach ($realUrlSiteConfigurations as $siteName => $realUrlSiteConfiguration) {
    foreach ($realUrlSiteConfiguration['languageDomainMap'] as $languageUid => $domain) {
        $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['realurl'][$domain] = $realUrlDefaultConfiguration;
        $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['realurl'][$domain]['pagePath']['rootpage_id'] = $realUrlSiteConfiguration['rootPageUid'];
        $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['realurl']['_DOMAINS']['encode'][] = [
            'rootpage_id' => $realUrlSiteConfiguration['rootPageUid'],
            'GETvar' => 'L',
            'value' => $languageUid,
            'urlPrepend' => $realUrlSiteConfiguration['schema'] . '://' . $domain,
            'useConfiguration' => $domain,
        ];
        $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['realurl']['_DOMAINS']['decode'][$domain] = [
            'GETvars' => [
                'L' => $languageUid,
            ],
            'useConfiguration' => $domain,
        ];
    }
}