The language is Bosnian as spoken in Bosnia and Herzegovina. Only 65% of Discourse is translated in this language: https://www.transifex.com/discourse/discourse-org/language/bs_BA/
To clarify for @RuxBux, when updates and new translations are submitted, it takes some time before they are manually pulled from Transifex into Discourse (usually by @techAPJ), the last one was 8 days ago:
https://github.com/discourse/discourse/commit/491c473e4eacd78adfdb64ab7933217f8bf4544f