This pakage contains the german core language files, modules, plugins and default themes for Cotonti Siena series. The folder /extra-plugins will contain translations for 3rd party plugins which I'll make for myself or upon request.
To install, just copy the folder contents over your existing Cotonti installation. This pakage contains both formal and informal versions, please grab the one that's best for your sites audience. Companies most likely want the formal version, as the informal version could be a little nonserious.