In Serbo-Croatian
Serbo-Croatian has a strong structural unity, according to the vast majority of linguists who specialize in Slavonic languages. However, the language is spoken by populations which have strong, different, national consciousness: Bosniaks, Croats, Montenegrins and Serbs.
Since the breakup of Yugoslavia in 1991, Serbo-Croatian has lost its unitary codification and its official unitary status. It is now divided into four official languages which follow separate codifications: Croatian language, Bosnian language, Serbian language and the Montenegrin language.
The common Serbo-Croatian system still exists in a (socio)linguistic point of view: it is a pluricentric language, being cultivated through four voluntarily diverging varieties, Croatian, Bosnian, Montenegrin, and Serbian, which are sometimes considered as Ausbau languages. However, Ausbau languages must have different dialect basis, whereas Croatian, Bosnian, Montenegrin and Serbian standard variants have the same dialect basis (Štokavian):
The problems of the so-called Ausbau-languages in Heinz Kloss’s terminology are similar, but by no means identical to the problems of variants. In Ausbau-languages we have pairs of standard languages built on the basis of different dialects . The difference between these paired Ausbau-languages and standard language variants lies in the fact that the variants have a nearly identical material (dialectal) basis and the difference is only in the development of the standardisation process, while paired standard languages have a more or less distinct dialect base.
Kloss contrasts Ausbau languages not only with Abstand languages but also with polycentric standard languages (Stewart 1968), i.e. two variants of the same standard, such as Serbo-Croatian, Moldavian and Rumanian, and Portuguese in Brazil and Portugal. In contrast, pairs such as Czech and Slovak, Bulgarian and Macedonian, and Danish and Swedish, are instances of literary standards based on different dialects.
On the contrary, the Serbo-Croatian kind of language secessionism is now a strongly consensual and institutional majority phenomenon. Still, this doesn't make it legitimate to say that such a language secessionism has led to "Ausbau languages" in the cases of Croatian, Bosnian and Serbian, since their diverging evolutions has not succeed in general practice:
The intercomprehension between these standards exceeds that between the standard variants of English, French, German, or Spanish.
Read more about this topic: Language Secessionism