New material is being produced all the time. This is a selective list of the main resources on Cultural Diplomacy from 2012 onwards that you could tap into on the Web, some of which are not as objective as they may seem.
The ICCE at Goldsmiths College London University together with the umbrella organisation ENCATC are very active in the area and have provided much of the material for this post.
The British Council continues to develop policy in this area. See one of their latest statements that trust pays, how international cultural relationships build trust in the UK and underpin the success of the UK economy
The Netherlands Institute of International Relations regularly publishes on the theme of Futures for Diplomacy – “integrative diplomacy” for the 21st Century.
EUNIC is a key organisation of European diplomats in post in the cultural institutes
Fergus Hanson produced Revolution @State: The Spread of Ediplomacy for the Lowy Institute in 2012
Rod Fisher with Carla Figueira regularly update their research for More Europe
Are you just starting on this? Here are the basic texts everyone needs to read: