How many programming languages do you need to learn ethical hacking?
Hacking is not like Web Development or Software development where you need specific tools to create something meaningful.
Hacking is like a mixture of different kinds of stuff that are combined together to crack the inner workings of the Technology. Even it's not only technical stuff sometimes it's social and psychological stuff that helps a hacker to achieve it's target(Social Engineering as specified in the answer above). It's just a word given to exploiting things. In Ethical Hacking you need to test the systems and provide security and for that you need to first breach them and for that you got to do some bad stuff.
If you really want to learn ethical hacking then you got to throw a deep dive into the ocean of technology which contains the inner workings of how these things work. How websites work? How do they Authenticate user logins? How Operating system works? What is a Network Topology etc. So I would first recommend you to learn about Networking like what is IP address, subnet masks, ARP, mac address, mac spoofing and then learn Some programming to keep your direction towards a Hacker and not Script Kiddie
But still if you are keen to know about the direction to start. I prefer learning Python because it has so many modules that can help you learn how hacking is done. Socket programming , Transferring files, sending emails can be just done in few Lines of code. Just google Python and it's features and modules and you will definitely consider working with it.
You should know how to operate Linux and get comfortable with it because Linux is Hacker's best friend and I would recommend you using Kali Linux because it comes loaded with about 300 tools that can help you in exploiting.