Translation of cscf_recaptcha is missing

When the reCAPTCHA option is enabled, the contact form will show the following message, if the form is submitted without solving the captcha first:

Please solve the recaptcha to continue.

A German translation for that message (cscf_recaptcha) is missing.

The other validation messages are translated correctly.

How or where can that be fixed?

A suitable German translation is:

Bitte l?sen Sie das reCAPTCHA um fortzufahren.