I’ve been tempted to call them my out-laws.
Well, if you want to take it there, the full meaning of what something means to me in my idiolect probably can’t be conveyed to you even when we’re speaking the exact same dialect of English. That’s the subjective dimension. But the full lexical meaning can always be conveyed objectively, and as for culturally-shared subjective impressions, that context can be provided by the translator too if required, at the cost of concision. Most likely in a footnote. A translator aims for the happy medium between crisp concision and readability balanced with fullness of semantics. The use of idiomatic expressions in the target language as well as the source language also fills in nuances. A good translator does not just produce an extremely literal word-for-word translation, but knows how to work in nuances of meaning from the source language into the target language.
I am not challenging the competency of translators or trying to get into a debate over whether anyone can ever know what anyone else ever truly meant in any spoken exchange.
You noted that the failure to communicate the meter and sound was what was meant by “lost in translation.” I merely noted that there was more to it than that. It would take much more than a footnote to explain to an audience just how powerful cursing was in the medieval period, (or even how powerful obscenities were to Americans in the 1950s.) And that is looking at texts in the same language. When there is a metaphor or simile that requires a familiarity with hardscrabble farming, footnotes can rarely achieve the same visceral response. Similarly, trying to translate not only the words but the intent and the feel of an expression from modern urban society to a society that has only the experience of subsistence farming is going to suffer a serious degradation in meaning, no matter how gifted the translator. Those are extreme examples, but Gemütlichkeit and Schadenfreude suffer some of that loss coming into American English and I suspect that a number of American terms suffer the same problem when taken into German, French, Italian, or Hindi.
This. I saw a claim that English has no translation of esprit d’escalier (diacritics lost to my imperfect memory). Of course it does: “staircase wit.” And if you’re going to object that that’s two words, French has no word for esprit d’escalier either.
(But German does: Treppenworter)
My impression is that this is what this thread is about: it’s interesting that Hebrew has no word for lap and English has no word for the “lap” created by your arms, even though you can describe those spaces in both languages. It’s interesting that Latin doesn’t distinguish between ceilings and roofs, but does between inside and outside walls. In these cases, even if some obscure word exists, it’s still interesting that it has remained obscure.
I don’t believe I’ve ever read “regular prose”, though, except maybe in a technical manual. Right now I am making semantic and syntactical choices that go beyond “meaning”–I’m striving for a very particular tone, using a particular style, developing a particular aesthetic. Hell, I just now spent a good two minutes making that last sentence into a parallel tricolon. I have no doubt that a good translator could translate the meaning of what I am saying. But to suggest that in ordinary prose there is nothing but meaning, no “extra-lexical dimensions”, is, I would argue, short-changing what writers do.
I wonder how a professional translator deals with ambiguity that is not possible in the target language.
Consider the following example in an work of fiction, source language English: After inheriting a fortune from an uncle ten years ago he had settled into a life of leisure. No further information on that uncle is available in the text.
Now that uncle could have been the protagonist’s mother’s brother, his father’s brother, and (as I understand English usage) also his mother’s sister’s husband or his father’s sister’s husband.
There are languages such as Turkish where there is no single term covering these four relationships (the terms AFAIK are dayı, amca, teyzemin kocası and halamın kocası, respectively). How would you go about translating the source sentence?
Another example: Swedish distinguishes between maternal and paternal grandparents so if I referred to a cake my grandmother baked for me this would probably be awkward to translate to swedish.
And to translate “brother” or “sister” into Japanese, you need to know if it’s an older or younger sibling – even if you’re talking about twins.
Ditto for Chinese.
“Jerk Store!” is also two words in English. 
Hopefully the translator will have access to the relevant information to be able to use the specific relationship term. In the absence of that, I don’t know, roll the dice or something. That’s an interesting question which I would like to pose to other translators. As for myself, I only translate from other languages into English, so I’ve never faced that problem.
Nevermind: responding to something earlier. Edited away to nothing.
It’s a bit contrived, but you could get the same problem with ambiguity sometimes translating into English. For example, since Hungarian does not distinguish male and female in the third person, a sentence like “Hazament” could translate as either “He went home” or “She went home”. Normally you could tell which to use based on context, but I could imagine situations or similar sentences, where you simply wouldn’t know which to use.