On the subject of "communication:"
Verbal communication is extremely complex and "feature rich" in humans. It is, by far, our most capable form of communication. We can shout over long distances, change our tone and pitch, place emphasis on certain words and change the entire meaning of them by doing so and we can sing or grunt with equal efficacy. Or vocal range is outstanding and our voices, themselves, are self-identifying - Anyone who knows us knows who it is that is speaking, even if they can't see us.
The human face is remarkable. How many antelope can you tell apart from just their "faces?" Both voice and face can be combined in complex displays that almost any human can understand. Some human cultures, however, have different interpretations of certain facial expressions. But, these are usually isolated cultures. Even so, there are prominent cultures that use specific facial expressions, so human facial expressions are likely heavily based on cultural/social adaption. Inflection and vocal emphasis, less so, due to more mechanical imperatives. (That shouldn't be surprising - Sexual Selection likely accounts for the greatest impact in the resulting diversity of human facial appearance.)
And, we can't underestimate other body movement/displays as communicating information, internal states, intent, etc...
Combining all of this represents the "very best form" of human communication. Examples of that can easily be seen on stage and screen or in an actor's studio where they are being taught by "Masters" at the craft.
All because we don't have functional "plumage." If we had feathers that changed configuration in response to an internal state, we'd be using those a lot too.
The written word is, of course, the most durable. It is also one of the most "sure" forms of communication when it is properly constructed and then read by someone who is fluent with it. There is little possibility for ambiguity or misunderstanding with the written word - It communicates what its creator intends it to communicate. We do not have to personally witness Marcus Aurelious's stoic expression as he communicates his information to us. Instead, we can completely comprehend the substance of his communication over 2000 years later simply by reading what he wrote.
Star Trek has implied different formats for a species's communication as well as different methods. But, the significance of those has always been difficult to translate to the audience. Who wants to hear grunts, growls, and then watch some tortured puppeteer have to animate hair rising? So, they have the "Universal Translator" and we do not have to try to interpret the color display and light-show of a Tholian pilot as it renders its judgement on the crew of the Enterprise... They get a nice tinny voice blaring from a speaker as interpreted by an on-board Universal Translator, instead.
Symbols last. They can be easily manipulated for maximum efficiency with the absolute minimum mastery necessary for use and interpretation. With enough symbols in a set that are easily understood by the user, they can communicate anything they wish for an appropriately armed audience. And, that's very important, too - A written language is predicated on the notion that it is being used by an audience that is capable of comprehending it.
I'm reminded of Hubbard's "Psychlos." Despite he, himself, being off-kilter, he was a great science-fiction writer. The Psychlos had a form of mathematics that could not be understood and it was the secret that guarded their most powerful technological capabilities - Teleportation. But, it's "math" and it should have self-evident "truths," right? Right! But... not Psychlo math. And, there was a reason for that which I won't reveal, but it is because the mathematics required privileged information that nobody but a Psychlo could possess. It was, in fact, not a fully logical and self-contained form of communication as anyone would think a rigorous system of mathematics should be.
That's brilliant "sci-fi" right there. The key to everything lay in something that the author sci-fi-twisted into something else, entirely.
IMO, if you want to think about forms of alien communication "realistically," then a lot of what is being communicated will rely on the assumed capabilities and knowledge of the audience. Aliens would likely choose to speak a form of "pidgin" instead of a fully voiced native tongue. Simple concepts may even be impossible to understand because the audience has no common ground that can be relied upon for a sure interpretation. Even so, shared principles that are immediately in evidence might be easy. "Ship go here" is pretty darn sure to be interpreted correctly. "Give me KFC Chicken" will not be.
Star Trek is a TV show. We'd get much more detailed and complex representations of "alien language" if it was a series of books. Special effects are easier to create with ink than lights, plaster, and latex.
