This is all getting a bit overwrought.
The use of morse was deliberate so that we could manage to understand and translate it.
It's near-infinitely more likely the Aliens would have their own language and own codes that we could barely dream of translating - they have thrown us a bone by using morse. Look at how many people complain about how hard that was to solve anyway - imagine what it would have been like if it had been an entirely new code in an entirely new language with entirely new names for all the planets etc?
It's deliberate to make the puzzle solvable by us. Just like the sounds can be heard at all - there's no sound in space. You'd hear nothing and any transmissions the UP/UA make are realistically going to be in the radio spectrum not audio, but it's put into the audio realm so we can solve it.