Site URLs with multiple sites in Craft 3

.env

SITE_URL_EN="@web"
SITE_URL_DE="@web/de"

general.php

<?php

return [
    // Global settings
    '*' => [
        'siteUrl' => [
            'english' => getenv('SITE_URL_EN'),
            'german' => getenv('SITE_URL_DE'),
        ],
    ],

    // Staging environment settings
    'staging' => [
    ],

    // Production environment settings
    'production' => [
    ],
];