1. More accurate forecast will be available 7-10 days before the Conference (It is expected around 20 C)
2. Belgrade is cheap city by western standards. You can buy a sandwich for 150-200 RSD (1 EUR ~ 115 RSD), Breakfast in restaurants is 500-1.000 RSD, same for lunch and dinner. Coffee price is 100-180 RSD, juices 150-200 RSD, a tea around 80-200 RSD.
3. From the airport to city center you may come with local bus, cab or airport bus. (More info here:Arrival)
4. Emergency help +381 (0)11 194, Police +381 (0)11 192, Fire Dept. +381 (0)11 193
5. Official language in Serbia is Serbian, a Cyrillic an Latin script in use. Most of citizen, especially youth speak and understand English, and they are familiar with German, Spanish, Italian, French or Russian.
6. Yes, majority of coffee shops, bars and restaurants have WiFi. Also, WiFi is available in some buses in city transport, hot posts, parks and squares.
7. Yes, there is. But avoid taking pictures of military buildings because it is forbidden.