I have read an article (https://helpx.adobe.com/indesign/kb/add_cs_dictionaries.html) about adding a Hunspell dictionary in inDesign and try to insert the Ancient Greek dic in InDesign but it was not working properly. I hope Adobe in the future to include and the Ancient Greek Language as there are many University Studies which teach Ancient Greek Literature and print books in ancient greek language. There is already a free hunspell dic so I suppose that it will be easy for adobe such a thing.