If you would like to develop your own blockchain, I would say that you need to learn C++. Instead of developing something from scratch, you might want to consider forking out of some of the opensource projects like Open source private blockchain platform, Bitcoin, or Ethereum.

If you want to develop smart contracts on top of Ethereum, you need to learn solidity. A good tutorial to get you started with developing dapps on solidity is: How to write your first smart contract in solidity

For Hyperledger fabric, you need to learn GO. Most of the chaincode (smart contracts in Fabric’s world) programming is done in Go. They also have a Java SDK at the moment.

Also, blockchain is just the underlying technology. You would always need some sort of frontend to give to your users to be able to interact with your applications. For that Javascript is probably the most important language to learn.