If you want to use German language please just change your WordPress language (Settings > Site Language) to Deutsch and then after some minutes you will see those translations on your WordPress updates section, click update and then Kalium strings will automatically translate to Deutsch.
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the language settings are already in german but the text " I’ve read and accept the terms & conditions "and the alert text is further in english.
Can you please share your site credentials here, because we need to login to your site and see this issue live. Your information is safe (private) in this thread.To include your credentials click Insert Credentials button in editor toolbar. (See how)