Exploring Altera product, would like to know what software skill is required.

Hi Vermeer, Hi level programming proficiency is of help if your company plan use multiprocessor and or DSP on FPGA, processor on hard soft core don't differ too much, soft core can be extended with special instrucion can speed up software and this require the second skill see more.

VHDL , Verilog are HDL languages:

for both hardware level knowledge are required and how computational structure work too, so it is a language for computer architect or hardware specialized.

Verilog seems a strange C++ but it is not a software, it generate hardware so see preceding line.

VHDL is the complex one, it can be a programming language, HDL and simulation, everything face to silicon hard or soft is covered by.

VHDL is a complex language not so user friendly as appear to be Verilog but I preferred VHDL over it is more clean, both are dangerous if you think as a computer programming language, Verilog is more compact but hide a lot of caveat of hardware.