Please give preference to those most widely used in the field, if possible.
A significant portion of SETI's work is done through a program known as SETI@home, which takes signals that have been received and processes them for responses, such as recurring patterns. Here is a page on how to download its source code. I grabbed the most recent nightly tarball and it turns out the program is coded in C++. I offer this as evidence that C++ is the most commonly used programming language used to process SETI's workload.