Which is an awesome idea and everything, but Russian, the language that developed from what the Rus spoke, sounds a lot more Slavic than it sounds, you know, Swedish.
So you can look at the third person of the past tense only as a list or you might, if languages that have cases, you can look at just the instrumental case, let's say in Russian or Slavic languages.
The same in Croatia, even though I spoke other Slavic languages and I worked a bit on my Croatian and I had a Croatian here, even a Serbian Croatian, it's more or less the same phrase book and nothing.