Relation between razor and riezati

I have no information about Old Slavonic, but I do know that Rome ruled the entire known world, and they all spoke Greek or Latin, and the unknown world all spoke some variant of Germanic. That is why students are told to learn Latin: it is the basis for almost all languages in the modern world. That is also why English often sounds so similar to German.

That does not mean that words are related, but you should not be surprised when they are.