@Sviatogor I can easily understand most of written Bulgarian (most Serbian speakers can, if they know what щ,я,ь,ю,ъ,й and э stands for, since Serbian Cyrillic doesn’t have those), it’s much harder to understand it in spoken form, because they speak really fast. There are definitely a lot similarities, especially with southern Serbian dialects, which also lack most cases,  I think Pirot dialect is closest to them. There is also division in South Slavic languages to Eastern South Slavic (Bulgarian and Macedonian) and Western South Slavic (rest of south Slavic languages) and Torlakian dialect somewhere in between.