well I am assuming here the message is going to be one of two either there are no results or you have not waited long enough between searches
at any rate if your using a custom language you must ensure your custom language has those language strings we added for the new search feature. A blank box means you do not have the language string entered. The inserts for the search strings are in the upgrade.php file
Knowing you run a german site I know this has to be your issue since we only release reviewpost in english.
anyway what I have stated in this thread is your error is because you have not input those language strings correctly for your custom language. I beleive if you changed your language to english you see the product works.
You must correctly insert those strings in german for the ones I posted.
You would have to follow the same procedure you did when you created your german language.
For example I posted the queries above. You could use phpmyadmin to import them into your german language but first what is your german language id number 2?
See the end of the queries
Content visible to verified customers only.
You need to change that one to whatever number your german language is probally number 2
Once you insert those language strings you will see the wording your missing.