What is ethical hacking and on which computer languages should I have command?

There is no official language for ethical hacking, but if you are interested in learning any language, you should go for Python and C. These two programming languages are really helpful in ethical hacking and penetration testing. Mastering any of the language is good for security professionals, apart from this you can also learn assembly language which is also a good language for ethical hackers.

If you are trying to get into web penetration testing then HTML, Javascript and PHP is really essential. You should also learn plenty of databases like mysql, postgresql, mangodb etc (at-least basic sql queries). If you want to dive more in programming/developing security tools then you can go for ruby, java, R etc.