Thank you all for your answers. I will have a look to the different projects you have mentioned in your emails. 

In the meantime I have spent a bit more time exploring Wikidata for paintings as one of our project currently focuses on Art and comparing it with the Europeana Data Model in terms of properties. I have noticed the absence of some properties and I would be curious whether it is just an overlook or whether there is a real intention behind the omission:

-Cultural Heritage data have most of the time a description property where you will find lot of relevant free text information. The structured property but inside you will find mostly free- text. I couldn't find a similar property in Wikidata but there is something similar in Dbpedia. Is it something you are planning to introduce or have you made the decision to exclude any free-text infromation from Wikidata for now. 

-While I was looking for painting in Wikidata I also noticed the absence of information related to the size/dimension of the Artwork. The information is most of the time present in Cultural Heritage data. Is it something Wikidata is interested in or has it been omitted intentionally? 

-Then the last question is about values in different languages for a given property. How do you indicate the language in Wikidata? Are you using a xml:lang attribute or something similar? 

Thank you very much for your help 

Best, 

Valentine