Did you know that when in the '70s NASA launched its Voyager space probes, a greeting in ancient Sumerian was included?

As long as they sent a Rosetta Stone along with it, great idea !

Yes, well known. I remember hearing about this in the 1970s.

Yes, it wasn’t considered a secret.Various languages were used as the government hoped that any other-world beings would be able to understand one or more of them.

It wasn’t so much hoping that an alien species would be able to understand one of the languages. It was just part of providing a little snapshot of human civilization. NASA doesn’t seriously expect an alien civilization to ever come across the Voyager craft. The Golden Records were really a nod to human romanticism among all the cold science. Knowing that the craft would be exiting our solar system eventually and most likely (barring unforeseen astronomical events) enter other solar systems NASA figured “why not?”.

Here is everything you’d ever want to know about NASA’s Golden Record on Voyager.
Here is a description of the contents.
“The contents of the record were selected for NASA by a committee chaired by Carl Sagan of Cornell University, et. al. Dr. Sagan and his associates assembled 115 images and a variety of natural sounds, such as those made by surf, wind and thunder, birds, whales, and other animals. To this they added musical selections from different cultures and eras, and spoken greetings from Earth-people in fifty-five languages, and printed messages from President Carter and U.N. Secretary General Waldheim.”

All 55 Greetings are listed here
Even Sumerian

Sumerian, not Babylonian.
Yeah, big difference!