Almost all the European languages belong to the family of Indo-European languages. So does Serbian. Together with Macedonian, Slovenian, Bulgarian and recently Bosnian and Croatian (and Montenegrin), Serbian belongs to the South Slavic languages. Serbian is based on the shtokavian (štokavian) dialect, which is sub-divided into Old and Neo-shtokavian, which are then divided into sub-dialects and further to local versions. Serbian language developed in two parallel ways – as a literary language, a standard writing one and the popular, colloquial one. As a literary language, it went from the Old Slavic, via Serbian Slavic and Church Slavic, to Slavic Serbian (spoken in the 18th and 19th centuries), to the modern Serbian literary language, which almost the same as the colloquial one. And during all that time, the popular (colloquial) Serbian, as any other language, was developing, changing and yielded oral tradition literature of a great value. In the 19th century, Vuk Kаrаdžić made a revolutionary change – he made the literary language of the period completely redundant, introducing the common popular one as the literary! So the standardisation started, resulting in the modern Serbian literary language used in speech and literature today. Vuk reformed the alphabet as well, erasing all the old characters that did not have any phonemic value. Thus the learned Serbs had to speak the common popular language, which yielded beautiful folk literature and which undoubtedly possesses great value, but lacks in numerous words, particularly in the area of spirituality. In the 19th century, officially by the 1850Vienna Literary Agreement, Serbian language gets adopted by the Croats, which after the WWII, would be commonly named Serbo-Croatian. After the breakup of Yugoslavia, new languages were proclaimed: Croatian and Bosnian, and of recently, Montenegrin. Truth be told, they are all Serbian language, as the shtokavian dialect borders are the borders of the Serbian language.
There are two different literary reflexes of Serbian – ijekavian (vjera, mlijeko) and ekavian (vеrа, mlеkо) (faith, milk)
The Serbs of Serbia speak both the ekavian and the ijekavian versions, and those in Republika Srpska and other parts of the former Yugoslavia, mostly ijekavian.