personally, I don't know. but there are talks regarding Paraguay as the "next" one to make bitcoin as a legal tender.
I also come across this news that Paraguay is considering legalizing bitcoin and also Honduras? not sure about the second but the first sounds legit.
But Serbia ? where did OP get this News , is there a valid reason or proof.
there are a lot of articles regarding the topic and people are making assumptions about it too. but at the end of the day no one really knows whether the "supposed next" country who will legalize bitcoin as a legal tender will ever do it.
It is still the people who lives in that specific country will decide.
Like what El Salvador did, when now Rallies and protest are happening because they did not get the pulse of their people instead they had pushed the law easily .