Orthanc is designed as a lightweight service for medical imaging, where the word service must be understood in the sense of service-oriented architectures. As a consequence, Orthanc is conceived as a robust back-end server (command-line) that aims to provide the most simple and generic support of DICOM. To state it differently, the primary focus of the Orthanc project is not on the user interface.
However, Orthanc comes out-of-the-box with Orthanc Explorer, its default Web user interface. Orthanc Explorer is designed for administrative, low-level purpose. It is also used by the development team to test the features of Orthanc as they get introduced in the REST API. Orthanc Explorer is mainly targeted towards an English-speaking technical audience (notably system/network engineers, PACS managers, medical physicists, and researchers).
It is possible that an official plugin that provides a more advanced user interface will be developed in the future (provided we find funding for this development). In the meantime, you can also contact a company that provides commercial support on the top of Orthanc and that might have developed an advanced user interface. Currently, Osimis is the only company ensuring such corporate services, but others might show up in the future. A contact form is available on the official Web page of Orthanc.