I found there are two versions of Serbian:
May I know what's the difference? Would someone please explain in details?
Linguistics Stack Exchange is a question and answer site for professional linguists and others with an interest in linguistic research and theory. It only takes a minute to sign up.Sign up to join this community
https://sr.wikipedia.org is for the Serbian language, in the Cyrillic alphabet (UPD: and in Latin, too: https://sr.wikipedia.org/sr-el/), in the Ekavian variety used in Serbia, “sr” stands for srpski — ‘Serbian’.
Serbo-Croatian is a pluricentric language with several local varieties, all of them very close and mutually understandable. After the breakup of Yugoslavia in the early 1990s, each of its former republics started using only its own variety and calling it its national language. The differences are numerous (in phonology, grammar, and vocabulary), you can read about them in detail here:
The best place to learn about Wikipedias is Wikipedia. Its article on Serbo-Croatian Wikipedia states:
The Serbo-Croatian Wikipedia was originally launched on 16 January 2002. [...] On 12 December 2002, a separate Bosnian Wikipedia was founded, later including articles from the original Serbo-Croatian Wikipedia. On 16 February 2003, separate Croatian and Serbian Wikipedias were launched.
Wikipedia's own newsletter The Signpost recently had an article on the much-publicized case of a takeover of Croatian Wikipedia, in response to a report commissioned and published by the Wikimedia Foundation. The article says:
The Croatian, Serbian, and Bosnian Wikipedias are unusual in that they all separated starting in 2003 from the Serbo-Croatian Wikipedia, which continued to exist. All these languages are mutually intelligible variants of Serbo-Croatian, which is termed "pluricentric".
The report states that
this structure enabled local language communities to sort by points of view on each project, often falling along political party lines in the respective regions. The report asserts, furthermore, it deprived the newly-created communities of editorial diversity that normally guides and underpins the traditionally successful process of editorial consensus in other pluricentric language projects.