Countries having official languages that is unique to their country of having official status.
A country having two or more official languages could only be considerable answer if all of its official languages is unique to their country of having official status.
Not so sure about Montenegrin though... It is part of the Serbo-Croatian dialect - which kinda means that you would have to include Serbia, Croatia and Bosnia into this quiz as well. None of them really have a unique language though as it is pretty much the same language. It would be like saying UK English and American English are different languages. Slovenia is slightly different though.
paraguay should be accepted imo, besides spanish, guaraní is also an official language there, as far as i'm concerned, no other country speaks that language (officially)