Toska – Russian – Vladmir Nabokov describes it best: “No single word in English renders all the shades of toska. At its deepest and most painful, it is a sensation of great spiritual anguish, often without any specific cause. At less morbid levels it is a dull ache of the soul, a longing with nothing to long for, a sick pining, a vague restlessness, mental throes, yearning. In particular cases it may be the desire for somebody of something specific, nostalgia, love-sickness. At the lowest level it grades into ennui, boredom.”
Mamihlapinatapei – Yagan (indigenous language of Tierra del Fuego) – the wordless, yet meaningful look shared by two people who both desire to initiate something but are both reluctant to start
Jayus – Indonesian – A joke so poorly told and so unfunny that one cannot help but laugh
Iktsuarpok – Inuit – To go outside to check if anyone is coming.
Litost – Czech – Milan Kundera, author of The Unbearable Lightness of Being, remarked that “As for the meaning of this word, I have looked in vain in other languages for an equivalent, though I find it difficult to imagine how anyone can understand the human soul without it.” The closest definition is a state of agony and torment created by the sudden sight of one’s own misery.
Koikumama – Japanese – A mother who relentlessly pushes her children toward academic achievement
Tartle – Scottish – The act of hesitating while introducing someone because you’ve forgotten their name.
Ilunga – Tshiluba (Southwest Congo) – A word famous for its untranslatability, most professional translators pinpoint it as the stature of a person “who is ready to forgive and forget any first abuse, tolerate it the second time, but never forgive nor tolerate on the third offense.”
Prozvonit – Czech – This word means to call a mobile phone and let it ring once so that the other person will call back, saving the first caller money. In Spanish, the phrase for this is “Dar un toque,” or, “To give a touch.”
Incidentally this is used all the time in India – a missed call, is a sign of everything from ‘I’m outside’, to merely, ‘you are far away and I am thinking of you’. Now I know what to call it…
Cafuné – Brazilian Portuguese – The act of tenderly running one’s fingers through someone’s hair.
Many of these lovely words have been collected at Altalang.com