Yes the rules vary embassy to embassy (this is not really unique to DTV, always been case for all thai visas except Elite, and that's because last one is not issued by embassys).

As to document language, again rules vary embassy to embassy, don't know rules of Italian embassys in particular but generally embassys accept documents in host country language, but again you have to look at details on individual embassy website AND look on fourms/groups like this to see if what embassy website says and reality match (regularly they don't).

General rule of thumb but not 100%, acceptable languages are Thai, host country language and English , some require official stamped (by your own gov) translations, most just require translations if not in the previous languages listed