The article starts with English, German, Spanish, Dutch, French, and Portuguese, which are described in sociolinguistics by the term "polycentric standard languages". In each of these cases, it is one language spoken by several nations in several countries, and there are certain linguistic differences between them, which are also reflected in codification, but they are not so many to consider ... [Show full abstract] them to be different languages. This is also evidenced by a very high degree of mutual understanding: fluent communication takes place between speakers of a polycentric language, regardless of nationality. The article shows that the term "polycentric standard language" can also describe the situation in Croatia, Serbia, Bosnia-Herzegovina and Montenegro. It also discusses culture, the name of the language, and the reasons why in these South Slavic countries there is a belief that they speak different standard languages.