show error string in german

public/API/queries/mailAddress.php

@@ -17,6 +17,6 @@ function mailAddress($hCaptchaResponse) {
     if($responseData->success) {
         return "$contactmail";
     } else {
-        return "Failed to verify Captcha";
+        return "Fehler beim Validieren des Captchas.";
     }
 }
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