Serbian accents
I know that parts of Serbia and Croatia distinguish different tones. Everything says that Serbian only has tone on long syllables except for this map, which says that short syllables are tonal in most of Serbia.
map: https://qph.fs.quoracdn.net/main-qimg-41637f75e6e658cefd4a18a417b62df4

Question

Serbian accents
I know that parts of Serbia and Croatia distinguish different tones.  Everything says that Serbian only has tone on long syllables except for this map, which says that short syllables are tonal in most of Serbia.
map:   https://qph.fs.quoracdn.net/main-qimg-41637f75e6e658cefd4a18a417b62df4

Answer

Don't bother with that stuff, my friend. It is actually one language, of which politics make three. For the sake of difference. My granddaughter of four years watches cartoons on all state television of the former Yugoslavia, without the help of an interpreter and subtitle. We older people only learned one language Serbo-Croatian or Croatian-Serbian. And we still have a great understanding today. Except the politics, of course. 
Good luck with the study!