Which is the best programming language to learn for hacking?

** Coming to choice of language for hacking, languages which support scripting are mostly used because one doesn't have to re-invent the wheel. Languages like Python, perl etc. have great supply of libraries which make things easy.
Tools which analyse data or packet capture(networking) etc. to understand how things work.**

code

For web app pentesting/hacking

HTML
Hypertext Markup Language (HTML) is the basics for creating web pages and other information that can be displayed in a web browser. So if you don't know HTML you should first learn it

JAVAScript
Learning java script. Will help you understand the basics of Cross Site Scripting

PHP/SQL
Majority of web applications are written using PHP and MySQL .So it is a must to learn PHP

For understanding exploits , shell codes,root kit etc

C & C++
More than 60 % of the exploits you will find on the web are written in C & C ++, Learning C & C++ will help you understand about Buffer overflows, Stack overflow etc, So learning C and C ++ is must for every hacker/Pen tester

Assembly
Learning assembly will help you in Writing/understanding Shell codes , Will Help you in Reverse Engineering applications and software's

For building tools and scripts

Python
Python is a very powerful high level language , Its Easy to learn and code, most of the tools and scripts for automation are written in Python . Knowing Python socket programming will help you a lot in Exploit writing

Ruby
Ruby is an another language which is used to write scripts, tools. Metasploit Frame Work is written in Ruby. so learning ruby will help you understand the in and outs of msf

Bash
Learning Bash is very Useful in writing small scripts for automation