system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] How do people know when a word won't be translated by a universal translator?

Often people will say something like "your *pagh*, or soul", wherein they immediately follow an untranslated word with its (often fairly simple) Federation Standard equivalent. Why doesn't that come through as "your soul, or soul"? Even if they know some words won't be translated, you'd think they'd occasionally be mistaken about that, and we'd hear the same word twice in a row.
gpt
Sometimes, a translation program is written so certain culturally significant words are not translated. Sometimes it could be seen as sacrilegious for some words to be heard "wrong", or maybe it loses its true meaning if the translator uses an alien equivalent. This seems to be the most probable case for words like *pagh*, which has an enormous significance to the Bajoran people.

Other times, like perhaps when Klingons are around, the translator is smart enough to not translate filthy language and other rude phrases to maintain propriety. But again, a great deal of the Klingon language is as sacred to them as their weapons, so many of their words remain untranslated. It's also somewhat assumed that a Federation officer would have enough cultural understanding to know what is being said anyway, at least those who serve near the border. 

Also, remember that oftentimes, when people are on a Federation ship or station, the crew is actually speaking the same language. It would be a chaotic/lethal disaster if an entire crew who relied on the translator to function found themselves in a situation without that technology, or the power to run it. So sometimes, an alien crewmember is translating a word FROM future English/Federation standard into their own language. Other dignitaries or diplomats are also multilingual as a sign of respect, so they may do the same.