The unique quirk with South Slavic languages is the linguistic work e.g. associated with Vuk Karadžić [1] which resulted in a cleaned up purely phonetic alphabet. This was done across the region and ended up getting plumbed through both alphabets, so e.g. the Croatians/Slovenes write in latin but with a handful of special characters for the unique sounds like "š" or the double-letter characters "dž" "lj", which also map 1-1 to stuff on the Serbian Cyrillic side.

It's the kind of legacy cleanup you love to see :-)

[1] https://en.wikipedia.org/wiki/Vuk_Karad%C5%BEi%C4%87