Bosnian, Croatian, Montenegrin, and Serbian (otherwise known as one language: Serbo-Croatian) are natively spoken by about 13 million people combined, primarily in Serbia, Montenegro, Bosnia and Herzegovina, and among Serbian and Montenegrin communities worldwide. They are integral to the cultural identities of their respective countries, known for their literature, traditional music, and shared history in the former Yugoslavia. Written in the Cyrillic alphabet or Latin alphabet, their grammar features a subject-verb-object (SVO) word order, a system of noun cases, and verb conjugations that indicate tense, aspect, and mood.
Stats
Language Family: Indo-European
Writing System: Cyrillic, Latin
Writing System Type: Alphabet
Writing Direction: L to R
Tones / Pitch Accent: 4
Morphology: Fusional
Cases: 7
Grammatical Gender / Noun Class: 3
Number of Verb Tenses: 7
Word Order: SVO
Number of Vowels (Monophthongs): 10
Number of Consonants: 25
Areas Where Spoken
Bosnia and Herzegovina (official) (84.1%) (2.89 mil)
Croatia (official) (96.1%) (3.71 mil)
Kosovo (official) (3.3%) (58 k)
Montenegro (official) (85.3%) (526 k)
Serbia (official) (90.2%) (6.00 mil)
Resources
Books
Easy Croatian textbook - https://ia601008.us.archive.org/23/items/easycroatian_r47/(Complete%20Book)EasyCroatian_r47.an.pdf
Serbian Grammar textbook - https://ruspalomnik.me/srpski/SERBIAN_eng.PDF
Step by Step Serbian textbook - https://is.muni.cz/el/phil/podzim2016/SB_01/um/Mira_Danilovic_-_Korak_po_korak_-_srpski-_Step_by_Step.pdf
Websites
https://croaticum.ffzg.unizg.hr/?page_id=5024 -> free beginner lessons by uni professors (English & Spanish);
https://hjp.znanje.hr/ dictionary (in Croatian so gotta know some)
http://pravopis.hr/ for spelling (also in Croatian) -> some spelling rules and explanations + a dictionary
Free online Croatian course subsidized by the government! https://a1.ffzg.unizg.hr/?lang=en