Bosnian, Croatian, Montenegrin and Serbian are official languages in Bosnia and Herzegovina, Croatia, Serbia, Kosovo and Montenegro. They belong to a group of languages called South Slavic Languages, a subcategory of the Slavic Languages. There are about 17-20 million speakers of Bosnian, Croatian, Montenegrin and Serbian worldwide. The language is also spoken in a big diaspora, mainly in Western Europe, the United States, Canada and Australia.
Both alphabets, the Latin and the Cyrillic, are used. The alphabet which is based on the Latin one contains 30 letters, including the following additional letters: č, ć, dž, đ, lj, nj, š and ž. The Cyrillic-based alphabet in use is very similar to the one used to write in Russian, however, there are some differences.
We are confronted with one polycentric standardized language, a language that is used by several peoples in several different countries with notable varieties (just like German, English, Arabic, French, Spanisch, Portuguese etc.) This fact becomes evident with the Shtokavian dialect, that serves as a common ground for the standard language and with the relations of similarities and differences inside the language and the resulting degrees of mutual intelligibility.
The use of four names for the standardised varieties (Bosnian, Croatian, Montenegrin and Serbian) does not mean that there are four different languages. All of the four modern standard varieties are equal and none of them could be considered a "main" standard variety. The fact that the language is a common polycentric one, gives every speaker the possibility to call it however they want to. The differences of the standard varieties and the differences in dialects do not justify a violent, institutional seperation. It is rather the opposite: They contribute to the enormous richness of one common language.