Try waiting a few minutes and reloading.
(Auf die Datenbank konnte nicht zugegriffen werden)
Backtrace:
#0 /var/www/html/includes/libs/rdbms/loadbalancer/LoadBalancer.php(937): Wikimedia\Rdbms\LoadBalancer->reportConnectionError() #1 /var/www/html/includes/libs/rdbms/loadbalancer/LoadBalancer.php(904): Wikimedia\Rdbms\LoadBalancer->getServerConnection(0, 'wiki', 0) #2 /var/www/html/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1049): Wikimedia\Rdbms\LoadBalancer->getConnection(-1, Array, 'wiki', 0) #3 /var/www/html/includes/GlobalFunctions.php(2463): Wikimedia\Rdbms\LoadBalancer->getMaintenanceConnectionRef(-1, Array, 'wiki') #4 /var/www/html/includes/cache/localisation/LCStoreDB.php(56): wfGetDB(-1) #5 /var/www/html/includes/cache/localisation/LocalisationCache.php(449): LCStoreDB->get('de', 'deps') #6 /var/www/html/includes/cache/localisation/LocalisationCache.php(495): LocalisationCache->isExpired('de') #7 /var/www/html/includes/cache/localisation/LocalisationCache.php(371): LocalisationCache->initLanguage('de') #8 /var/www/html/includes/cache/localisation/LocalisationCache.php(312): LocalisationCache->loadItem('de', 'fallbackSequenc...') #9 /var/www/html/includes/language/LanguageFallback.php(106): LocalisationCache->getItem('de', 'fallbackSequenc...') #10 /var/www/html/includes/language/LanguageFactory.php(175): MediaWiki\Languages\LanguageFallback->getAll('de') #11 /var/www/html/includes/language/LanguageFactory.php(121): MediaWiki\Languages\LanguageFactory->newFromCode('de') #12 /var/www/html/includes/ServiceWiring.php(241): MediaWiki\Languages\LanguageFactory->getLanguage('de') #13 /var/www/html/vendor/wikimedia/services/src/ServiceContainer.php(447): Wikimedia\Services\ServiceContainer->{closure}(Object(MediaWiki\MediaWikiServices)) #14 /var/www/html/vendor/wikimedia/services/src/ServiceContainer.php(416): Wikimedia\Services\ServiceContainer->createService('ContentLanguage') #15 /var/www/html/includes/MediaWikiServices.php(623): Wikimedia\Services\ServiceContainer->getService('ContentLanguage') #16 /var/www/html/includes/Setup.php(700): MediaWiki\MediaWikiServices->getContentLanguage() #17 /var/www/html/includes/WebStart.php(89): require_once('/var/www/html/i...') #18 /var/www/html/index.php(44): require('/var/www/html/i...') #19 {main}