Hello, @Oliver Theiß,
Actually, that string is not from our theme but your site’s third-party plugin “WooCommerce Dynamic Pricing & Discounts” and I can see it is already translated in the plugin language files as well: https://www.optimumcore.eu/wp-admin/admin.php?path=languages%2Floco%2Fplugins%2Frp_wcdpd-de_DE.po&bundle=wc-dynamic-pricing-and-discounts%2Fwc-dynamic-pricing-and-discounts.php&domain=rp_wcdpd&page=loco-plugin&action=file-edit but not reflecting on your site, might be that is not translatable or any issue from the plugin, so I suggest you to please reach out to the plugin support for this issue and ask to fix it.
Regards 8Themes Team.