An Oman Air Airbus A330-300, registration A4O-DI performing flight WY-123 from Muscat (Oman) to Munich (Germany), was enroute at FL380 about 160nm northeast of Sofia (Bulgaria) in Romanian Airspace when the crew decided to divert to Sofia reporting a smell of smoke in the cabin. The aircraft landed safely on Sofia's runway 09 about 35 minutes after leaving FL380. The occurrence aircraft remained on the ground in Sofia for about 23 hours, then continued the flight as WY-123D and reached Munich with a delay of 23 hours. The airline reported smell of smoke prompted the flight crew to divert the aircraft to Sofia.