It is a good article, but the name is misleading. Albanian, Greek, Romanian are not Slavic languages at all. There is also Turkish, and few other minor languages spoken.

This article should be named: "What language do people in former Yugoslavian countries speak"

More than half of the Balkans are not slavic.

As for slavic languages: Croatian and Serbian are pretty much the same, and Bosnian is similar close enough. Slovenian is slightly different, then there is Bulgarian. Macedonian is just a dialect of Bulgarian language.

Non slavic languages:

Albanian - Isolate of indo-european languages (its own branch)

Greek - its own branch of indo-european languages

Romanian - Latin branch, with some Dacian (less than 2%)

Other Minor Languages: Turkish, Romani Variants, etc - (aka, i.e. not to be confused with romanian, but it is an indian origin language)

As for the whole peninsula, they share a lot of common words due to the ottoman empire's past, which is called a Balkan Sprachbund https://en.wikipedia.org/wiki/Balkan_sprachbund

Even they might share some words, name of objects, or food dishes, A Greek, an Albanian, a Slavic, and a Romanian person will not be able to understand each other at all.