The ones about home and table
Sobremesa (Spanish): the time spent lingering at the table after the meal is finished, talking. The meal's real second course. Hygge (Danish): the quality of cozy contentment, candles, wool socks, no agenda, that Denmark built a national identity on. Lagom (Swedish): not too much, not too little; the exactly-enough amount. The Swedish answer to a question Goldilocks asked and English never resolved.
The ones about longing
Saudade (Portuguese): the bittersweet longing for something absent, a person, a place, a time, that may never return; fado music is this word with strings. Fernweh (German): farsickness, homesickness for places you've never been. Natsukashii (Japanese): the warm flush when something small summons the past fondly, closer to a smile than to grief.
The ones about people
Schadenfreude (German): joy at another's misfortune; English gave up and borrowed it whole. Sitzfleisch (German, literally "sitting flesh"): the ability to sit still long enough to finish difficult work. A word for a virtue English pretends is just discipline.
The ones for readers
Tsundoku (Japanese): acquiring books and letting them pile up unread. If this word found you personally, we can't help; we publish books specifically designed to be read one page at a time, which is either the cure or an enabler. Wabi-sabi (Japanese): the beauty of the imperfect and impermanent, big enough that we gave it its own guide.
The deep cuts
Ubuntu (Nguni Bantu): the idea that a person is a person through other people; humanity as something we grant each other. Yūgen (Japanese): the profound sense of the universe's depth triggered by something glimpsed, not explained; the feeling the best Zen art aims at (our Zen primer circles it).
Why some words never translate
A word survives where a culture keeps needing it: Denmark needed hygge the way Portugal needed saudade, and the word then teaches the feeling back to new generations. English, meanwhile, has been quietly losing words this good for centuries; rescuing them is the entire premise of 365 Days of Forgotten Words (ours: one lost English word a day, from absquatulate to zemblanity, ★4.8 on Amazon). English once had words this precise; our 12 forgotten English words makes the case they deserve the same rescue.
Common questions
What is the most famous untranslatable word?
Probably saudade (Portuguese), the bittersweet longing for something absent, or hygge (Danish), cozy contentment; both are so useful English has begun borrowing them untranslated, as it long ago did with schadenfreude.
What does tsundoku mean?
Japanese for acquiring books and letting them pile up unread. It carries no judgment in Japanese, which is perhaps why book lovers everywhere have adopted it with relief.
Are untranslatable words really untranslatable?
They're translatable by sentence, just not by word: English can describe saudade but needs a paragraph. The interesting part is what a culture chose to compress into a single word, because that marks what it needed to say often.
Does English have words other languages lack?
Plenty: 'serendipity' is notoriously hard to translate, and English's lost vocabulary is full of one-worders like 'apricity' (the sun's warmth in winter) that other languages would envy; rescuing those is its own project.