After hours of research, emailing and testing I finally got a working and clean search engine in opencms. The problem I (and many others had and still have) is, that OpenCms/Tomcat/productX re-encodes a query string to ISO-8859-1. But lucene and Opencms store the search index in UTF-8. So this is a big problem, because the search list has not the real querystring the user entered anymore.
I decided to create a little how-to for any opencms user with the same problem. If you have any problems or feedback, please let me or the mailling list know.
Hope this helps you