Reading through the comments for this submission, I can't believe how many people didn't understand the specific phrase "on some Slavic shit".

The phrase "on some shit" comes from the United States, from urban AAVE (African-American Vernacular English). There's another commenter that refers to the phrase as 'hip hop lingo', which isn't too far off, but I think it's the wrong label.

The origins of the phrase are hard to pin down, but nowadays you'll see the idiom as "on some ____ shit", where you replace the blank with just about any noun or adjective. It has a fairly wide range of meaning, but the gist is 'acting ____', 'referencing ____', 'influenced by ____', 'in the style of ____' .

In this article, writing about Romanian language, saying, "[they're] on some Slavic shit" means "[they're] influenced by Slavic" or "[they're] referencing the Slavic style".