We feedbacked that:We found your site is different from magento default so if you want to translate, you should run command to render texts into csv files:
php_cli bin/magento i18n:collect-phrases -o
It did generate to a new file app/design/frontend/[theme]/i18n/de_DE.csv included text into translate function but you should rewrite the text that you want to translate on this file
For more information about product, please refer Quantity Dropdown for Magento 2 page.
If you need any further assistance, please feel free to contact us.
Please visit our site for more useful Magento 2 Extensions: https://bsscommerce.com/magento-2-extensions.html