The universal translator, that handy gadget that lets our heroes talk to and understand just about anybody. One problem, it doesn't seem to work on certain words. Take Klingon, Ptak, and Topah. (Sorry for the spelling here, Klingon language buffs.) Now we know that these are swear words, so you couldn't have the translations on a TV show, but is there an in-universe explanation why we don't hear "targ fornicator", or words to that effect?
Not all words and phrases have exact counterparts in other languages. Deanna once made the example of the phrase "Juliet on the balcony." A Klingon hears through his UT "female name - standing upon - a platform." The UT would have to at least summarize the first act of Romeo and Juliet for "Juliet on the balcony" to accurately describe Juliet's feelings of romance and teenage angst.
What really gets weird is when a Klingon says a Klingon word, and then offers an English translation. For example, very often we hear Worf say something like "It is known as the cha'nob vo' 'Iw, which translates as the offering of blood." Why didn't the UT kick in and instantly translate cha'nob vo' 'Iw as offering of blood?
^^^ But I find myself doing this on occasion. This past November, I found myself explaining the significance of Día de Muertos (Day of the Dead) to a fair number of people when I would mention it in conversations. Maybe it has to do with proper nouns. The translator may be advanced enough to know when someone is using a ceremonial term, and that it isn't supposed to translate it. The same with saying someone's name, every time I would use my family name, the UT wouldn't jump in with "one who baptizes" Many people's names have meanings. Cha'nob vo' 'Iw could also have multiple meanings, depending on usage, and the UT doesn't know which one to render. Worf then supplies the usage he specifically was referring too.
I'm sure that the context of the situation would matter. For example; If Worf, a Starfleet officer, was talking to Riker and Picard, also Starfleet officers. Why would the UT take any part in the conversation? The UT should assume that officers in the same service or an ally would probably know how to communicate with each other. Unless specifically instructed otherwise.
There was an interesting episode of Farscape, where all the main character loss the use of their translation microbes. None of the them spoke any of each others languages. When Worf is surrounded by other Klingon, I would assume that they are all speaking a Klingon dialect. When Deanna and Laxanna are in private, surely they're speaking a Betazed language. If everyone one on TNG were speaking different languages, and hearing others through their UT's, that would be kind of cool. What is Beverly Crusher actually speaking most of the time? Gaelic? Certainly in the episode that took place on the Scottish culture colony, the locals were speaking it. The Native Americans who left Earth to preserve their culture, they were speaking English? I've alway thought that Major Kira wasn't speaking English, not any at all. In the first episode of DS9 my impression is that she was assigned to the station at short notice, and her disdain for the Federation in general certainly wouldn't have lead her to previously learn one (of thousands?) of the Federation member languages. But she spoke English better than I do. That Kira would have learned Cardassian I could see, but English? Picard: "Le thé, Earl Grey, chaud."