Languages: Serbian (the majority), also Hungarian in the north.
The Serbian language similar to with Croatian and Bosnian. Before the era of nationalist linguistic policies and the breakup of the former Yugoslavia, they were all known as Serbo-Croatian. Today people in the former Yugoslavia no longer use this general term for what remains a common language.
English is commonly spoken throughout Serbia and the younger people tend to have excellent command. They are also quite willing to practice it with foreigners. Also you can try with young people talking German, French or Spanish which are learned in Serbian schools.
If you speak Russian it can prove to be occasionally helpful for you. Even though Serbia has never been politically involved with Russia, the two languages have some similarities. This also includes all other slavic languages, especially Bulgarian and Macedonian.
In Vojvodina most people speak Serbian, but other languages are also used. In some towns near the Hungarian boarder you are more likely to hear Hungarian. There are many smaller minorities, like the Slovaks, the Romanians, and the Russians, etc. who often speak their native languages as well.