Looking at using CiviCRM in an office based in Germany with German-speaking staff. Is there a localised version available, e.g. admin interface in German?
Yes there is, for more information about downloading translations please see: https://civicrm.org/download-translations
The installation instructions for localized versions vary depending on the CMS you will be using. But full information can be found here: https://wiki.civicrm.org/confluence/display/CRMDOC/Installation+and+Upgrades
You can changed the language by including
l10 packages under directory;
civicrm/l10 and with following;
Also you can set the Default Language
,country and states