Ah, an expositionist.
Whether a person’s mouth moves in sync is not critical to the functioning of a UT.
Obviously, visually in a TV show, it’s a lot to ask them to have virtually everyone’s voice out of sync with their mouths (or, say, spock speaking vulcan the whole time with subtitles but everyone on board can understand him, after a delay).
But the idea of an earpiece / speaker that translates known languages is not only feasible, you can buy such translators right now, with accuracy improving all the time.
For unknown languages, I would agree that the “brainwave” handwave doesn’t work, but we can certainly speculate on non-magical mechanisms.
I imagine we could hand a species some kind of tablet, that would explain some basics about us, visually and interactively, finishing with illustrations of how we can (digitally) share data on our languages.
It’s a common meme that “We can’t speak to cuttlefish, what hope would we have of speaking to aliens?”, but the truth is, for a species to develop interstellar travel, they would have to have a general intelligence, that they can apply to complex abstract problems wholly unlike those experienced in their evolutionary past.
For such a sentient species, decoding structured data, that another sentient species is actively trying to help you decode, can be filed among “easy problems”.
No, he was dying when he arrived there, and it (she?) healed him and made him young again: Metamorphosis (episode) | Memory Alpha | Fandom.
That’s about how I imagined it.
As good as that episode was (particularly for introducing a whole lot of Trekkers to the tales of Gilgamesh), I never bought that an advanced starfaring civilization could or would communicate solely by metaphor. There are times when you need to say “Come to heading 435 mark 7” or “Pass me that wrench,” and metaphors get you only so far.
Sensors on the doorframes, naturally. Of course, they’re not foolproof - see here at 2:16: https://www.youtube.com/watch?v=hBQi7VXsT8Y
Talk about handwavium…
The UT can translate the speaker’s voice into the hearers’ native language.
This is a situation where Star Wars beats the spandex pants off of Star Trek. For a group of spacefarers, something like a protocol droid would be absolutely essential. Not just to handle language barriers, but also to anticipate and deal with the inevitable cultural clashes that would arise. (That’s what they mean when they call C3PO a “protocol droid.” His primary function is diplomatic.)
This was sort of retconned in the final episode of ST Enterprise, when they show Sato working on what I assume is the prototype for the first Universal Translator; she can’t get it to differentiate between two particular languages. If it detects brain waves, rather than converting words directly, then this shouldn’t be a problem.
Then again, for all we know, this approach was dropped in favor of the “brain waves” one.
Boobies. Troi was there for boobies.
P.S. I read through the entire thread to make sure that wasn’t already said.
I think it was retconned long before that - with Darmok, and Sanctuary (the DS9 episode mentioned above).
¿Que?
Comic Book Guy, his words aloof.
VarlosZ, his disbelief suspended.
A few linguists of my acquaintance have a working familiarity with common adversary languages other then their working focus, so it’s not impossible.
They’re voice activated.
Thanks for the props, gnoitall.
I admire your diligence.
Being familiar with a language does not mean you’re qualified to translate it. I speak as a professional translator.
It shouldn’t be a problem, no, because you can’t translate merely by substituting one word for another. You must convey the thought.
Would you bet your life and the peace of the Galaxy on one?
Why not? 
I speak pretty damned good Spanish, with a specialty in my career language, and translation between English and Spanish (either way) is one of the most scary, horrible things that I can image. Perfect comprehension and perfect ability to speak do not imply the ability to translate. I don’t even mean in real-time. Just translate, period. I admire people who can translate.
For others, I don’t mean piddly shit like, “How much does this cost?” I mean intense conversations where much of the language is unspoken.
In the not-too-distant future as the technology greatly improves? Sure.
Especially since such software will eventually supersede “native” level. For example, even a native speaker will occasionally be misunderstood or misinterpreted. A powerful AI could cross-check everything it’s saying against possible misinterpretation, and have detailed stats on what sentences are absolutely clearest in meaning.
Also, obviously, a better vocabulary, so it will understand our guests whether they use archaic terms or the latest slang.
- Brain signals are a very coarse signal produced as a side effect of brain activity. Not some kind of code.
- Everyone’s brain is wired somewhat differently.
Experiments where, say, we work out whether someone is thinking of red or blue, have to be trained to a specific person’s brain by showing them just red and just blue many times. - We would not expect alien physiology / neurology to mirror our own so closely.
Re: #3 - Trek Canon implies that, in many cases, they do. See my name and even telepathy/empathy used by Vulcans, Betazoids, and others.