Yagan
When two individuals wordlessly share a look that indicates interest, but both are hesitant to make a move.
Russian
As Vladmir Nabokov describes, “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.”
As Milan Kundera explains, “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 definition is similar to misery, being distraught over one’s own sense of pain.
Brazillian Portuguese
Running fingers through someone’s hair with gentle, tender care.
Japanese
A word that is both a feeling, an aesthetic, and an understanding of the world around us. Loosely translated, it means an understanding and acceptance of the cycle of the world—life and death, grow and decay. It is finding light in the darkness, or beauty in imperfection. It is understanding that the world is ever-changing, and things will come and go.
Arabic
Best translated as ‘You bury me.’ Both heartbreaking and lovely, it means that you simply cannot live without someone because of how deeply you love them.
German
The fear of getting older, of losing out on life experiences or moments with age. The literal translation is ‘gate-closing panic,’ or being scared of diminished experiences as one goes through life.
Spanish
Looking at art or something in nature and being unexplainably, deeply moved.
Porteguese
A longing for someone whom you loved and lost. 
Marisa Donnelly is a poet and author of the book, Somewhere on a Highway, available here.
Author Disclaimer: Definitions are my own modifications, unless otherwise noted.