They are not. South Slavs can't understand East Slavs. Western Slavs don't have a clue what Eastern Slavs or Southern Slavs are talking about, and vice versa. Not to Mention Hungarians, Slovenians, Albanians, Romanians, Bulgarians, Greek, they couldn't make sense of most Slavs are on about. Go back to school or start travelling.
I wasn't backpacking, I was in a peace mission you fool.
If you join any Slavic Facebook group you will see that they are mostly communicating in English, there is a reason for it, they can't understand each others.