Actually, "медведь" is not a real name of this beast. It is also a nickname, the real name is lost in time.
This kind of superstitions was very widespread everywhere.
No, AFAIK this is specifically Judaic tradition and it is related to Kabbalah somewhat. It was assumed that the essence of holy texts (Torah) are not to be understood by the human mind, and people should follow the instructions literally. So Torah says "Don't mention in vain the name of God". OK, but it says nothing about mentioning in vain some substitutes. Everything that is not prohibited, is allowed. A kind of pettifoggery, if you ask me.![]()