Change language in message to subscriber?

Hello,
I successfully installed the plugin (thanks for the plugin) and changed everything I could in the forms-section. But that stops right on the website; everything that happens after submitting is still in English (the mail to the subscriber and the double-opt-in forms the subscriber has to confirm).
I checked the .mo- and .po-files but couldn’t find anything there. Where can I translate these text-fragments (e.g. “Subscription Confirmed
Your subscription to our list has been confirmed.”)?

https://www.ads-software.com/plugins/mailchimp-for-wp/