Which programming languages are supported to program Arduino?

My advice, stick with the C++ derived Arduino language or use raw C/C++. It's ideally suited to microcontrollers. But, if you like esoteric languages:

• Occam via concurrency.cc
• BASIC via DK-Basic
• Java via NanoVM
• Forth via amforth

you can use the language that you feel more confortable, then you can look for a way to compile in arduino code machine. For example I use Go Lang and I use gobot.io to do it working...

Exist Cylon.js if you want to program in JavaScript or Artoo for Ruby developers.

Actually C is the most common because the IDE of arduino work with it.