Montenegrins speak and write Montenegrin. It is sociolinguistically, ethnically, and culturally a separate language. For example, the Montenegrin language has 33 letters while Serbian has 31 and Croatian and Bosnian each have 32.
The Montenegrin language evolved from an ancient Slavic language. It shares the same linguistic origins as the languages of the Croats, Serbs and Bosnians, but with distinct lexical and phonetic characteristics. These characteristics, which define its identity, are easily recognized and give it a national individuality.
Because this language was created by Montenegrin people, the only possible name for it is Montenegrin just as other Slavic languages are named after the people who speak them. The spoken form contains different dialects used by Montenegrins in different parts of Montenegro. Both within and outside of Montenegro, the term Montenegrin is used every day. The traditional Montenegrin language is characterized by a tendency toward proverbs, metaphors and condensed, figurative speech.
Before the South Slavic linguistic reforms begun in 1863, the traditional Montenegrin language was used freely, naturally and spontaneously and so developed to a high level of creative expressiveness, as manifested in the rich oral literature and in the works of the genius poet Njegos. Njegos's writing captured this original Montenegrin language. His work included local dialects, provincialisms and neologisms. He exercised wide freedom in the use of language - like all great writers, who are essentially creators of language and for whom anything artistically functional is correct and beautiful.
In the middle of the 19th century, the language of the south Slavs was reformed. The reform was based on Vuk Stefanovic-Karadzic's faulty premise that the language of all South Slavs, not only that of the Serbs, Croats, Montenegrins and Bosnians but even that of the Macedonians and Bulgarians, belonged to the same linguistic group - Stokavski. This premise was based on the fact that they can communicate together to a greater or lesser degree. To Vuk Stefanovic-Karadzic, correct meant "widely in use". Everything that did not fit within this "norm" was declared incorrect and non-literate; for example, three sounds unique to the Montenegrin language (that are used in spoken lagnuage even today) were left out of this standardization. This created an artificial division between oral and written language. Even today in Montenegro, many older people and village folk still use the original non-standard language, which is generally more expressive and poetic.
Karadzic and later Alexandar Belic and the Serbian Academy recognized Njegos as the greatest poet of the South Slavs. Yet their linguistic reforms in many ways undermined the extraordinary quality and expressiveness of Njegos' unique language.
Please see http://www.montenegro.org for more information