Fatal error: PHP error in file /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/util/StringUtil.class.php (423): Array and string offset access syntax with curly braces is deprecated

Information:

error message: PHP error in file /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/util/StringUtil.class.php (423): Array and string offset access syntax with curly braces is deprecated
error code: 0
file: /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/system/WCF.class.php (255)
php version: 7.4.20
wcf version: 1.0.11 pl 1 (Horizon)
date: Tue, 15 Jun 2021 15:27:21 +0000
request: /
referer:

Stacktrace:

#0 /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/core.functions.php(29): WCF::handleError(8192, 'Array and strin...', '/srv/www/vhosts...', 423, Array)
#1 /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/core.functions.php(29): require_once()
#2 /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/system/cache/CacheHandler.class.php(48): __autoload('StringUtil')
#3 /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/system/WCF.class.php(285): CacheHandler->addResource('languages', '/srv/www/vhosts...', '/srv/www/vhosts...')
#4 /srv/www/vhosts/no-kill.de/httpdocs/lib/system/WBBCore.class.php(80): WCF->loadDefaultCacheResources()
#5 /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/system/WCF.class.php(278): WBBCore->loadDefaultCacheResources()
#6 /srv/www/vhosts/no-kill.de/httpdocs/wcf/lib/system/WCF.class.php(90): WCF->initCache()
#7 /srv/www/vhosts/no-kill.de/httpdocs/global.php(18): WCF->__construct()
#8 /srv/www/vhosts/no-kill.de/httpdocs/index.php(7): require_once('/srv/www/vhosts...')
#9 {main}