The Universal Translator to my knowledge was audio only, for spoken languages. There was no UT for written language if I recall. How did the crew know what button to press and how alien UI even worked? Especially for aliens of the week that they have never met before? I have certain theories, but what do you think they used to translate written Alien Languages?
I'm not familiar with any reference for the UT being unable to translate written language. Sometimes it struggles with that, obviously. But sometimes it struggles with spoken language, too. And contrary evidence certainly abounds: Tom Paris is fluent in Kazon displays in "Investigations", say. And sometimes the UT built into our TV sets is at work, allowing us to read Klingon/Organian in "Errand of Mercy" or Blinkian in "Blink of an Eye" as if it were English. Timo Saloniemi
But what if it's a brand new species with a language that you have never seen or heard before? How does it figure it out?
I know that, but how does it display that info to the user? And what if it's a brand new language that it has no new info on? How does it go about figuring it out?
As an example, assume you are in an alien ship. You download data to your ships computer,which does the work of translating. Use that knowledge to translate alien displays into Standard.
How does it display spoken word to the user? Obviously not through a mere loudspeaker (except in the very earliest stages of translation, in especially challenging cases, such as ST Beyond, where the baddie was probably deliberately making it extra difficult anyway), since we don't hear "doubletalk". And we even see lipsynch. So the obvious interpretation is that the UT implant ties directly into the brain, making the hero hear and see her own language. Our brains are easily fooled like that. Lipsynch and English print are just two sides of the same coin. It's a clever beast, is all. The ultimate cryptographer, working not just from what it sees or hears, but from a background database of eleventeen zillion known languages and other cues. Episodes like "Contagion" show that languages in the Trek Milky Way get affected by each other just like languages on Earth - while episodes like "The Chase" show that all the great minds think alike because all our brains are a vanity project for ancient humanoids. This must be a great relief for the UT. Timo Saloniemi
It could depend on the person, Chief O'Brien could read every Cardassian panel on DS9 in short order, but then he also fought in the Cardassian War and may well have a knack for the language. Everyone else would have had to learn it some other way, Bashir could do so quickly as we know, Dax might have learned it with a different host, but others wouldn't have had any reason to know before they went to DS9.
I'd say the best example of what the OP is talking about is TSFS, the brief scene of Chekov, Sulu, and Scotty all huddled over the Bird of Prey's helm, knowing which buttons need to be there because they know how starships work generally, and trying to puzzle out what the most logical place for the things they need on the console in front of them. I suppose if you boil it down (and don't have a visual UT handy, or the controls you're using are unlabeled or encoded somehow), you can just count on the fact that the most basic stuff carries over, and you can get away with not having a mastery of the details, at least for a little while. Another example would be in the early nuBSG episode, where Starbuck commandeers a Cylon Raider and figures out that its various tendons and muscles correspond to different functions of the ship, and that all she needs to do to get off the moon and draw enough attention to be picked up is to figure out which ones pitch the ship up and down, roll it left and right, and control the engine throttle. And there's the case of Soren's rocket in Generations, where when Picard was sabotaging it he did take the step of switching the interface to english, so we audience members could read how he'd hoisted Soren by his own petard right before he blew up.