South Slavic languages follows Old Church Slavonic
History
The first South Slavic language to be written (also the first attested Slavic language) was the variety of the Eastern South Slavic spoken in Thessaloniki, now called Old Church Slavonic, in the ninth century. It is retained as a liturgical language in Slavic Orthodox churches in the form of various local Church Slavonic traditions.Classification
The South Slavic languages constitute a dialect continuum. Serbian, Croatian, Bosnian, and Montenegrin constitute a single dialect within this continuum.
Eastern
Bulgarian – (ISO 639-1 code: bg; ISO 639-2 code: bul; SIL code: bul; Linguasphere: 53-AAA-hb)
Macedonian – (ISO 639-1 code: mk; ISO 639-2(B) code: mac; ISO 639-2(T) code: mkd; SIL code: mkd; Linguasphere: 53-AAA-ha)
Old Church Slavonic (extinct) –  (ISO 639-1 code: cu; ISO 639-2 code: chu; SIL code: chu; Linguasphere: 53-AAA-a)
Transitional
Torlakian
Western
Slovene (ISO 639-1 code: sl; ISO 639-2 code: slv; ISO 639-3 code:  slv; Linguasphere: 53-AAA-f)
Kajkavian (ISO 639-3 code:  kjv)
Chakavian (ISO 639-3 code:  ckm)
Serbo-Croatian/Shtokavian (ISO 639-1 code: sh; ISO 639-2/3 code: hbs; SIL code: scr; Linguasphere: 53-AAA-g).There are four national standard languages based on the Eastern Herzegovinian dialect:
Serbian (ISO 639-1 code: sr; ISO 639-2/3 code: srp; SIL code: srp)
Croatian (ISO 639-1 code: hr; ISO 639-2/3 code: hrv; SIL code: hrv)
Bosnian (ISO 639-1 code: bs; ISO 639-2/3 code: bos; SIL code: bos)
Montenegrin (ISO 639-2/3 code: cnr; SIL code: cnr)