People use different languages for different things.

If it is extremely CPU intensive then people use C++ or CUDA.

For things involving exchange of data, then people start using Java.

Then for high level research/prototyping people use python, R, and I've seen Matlab.

For reporting and bookkeeping people use Excel/VBA.

All of these languages are interconnected. So you could have someone write a C++ pricer, punch that into a Java trading system, then analyze the data with Python or R, and then dump all of that into Excel/VBA.