The Access Control on tasks can organise this if you set the tasks up correctly (assign role w/ access where name like ROLE:German...).
The other option is to play around with the object filtering. On the MX_PERSON object (and all others) under the General tab you'll find the Access Limitations section.
You can use this to limit the access of administrators to certain subsets of data. Check the online help for more details. They have an example there which may help.
Peter