Some interesting examples of concepts that have a word in foreign languages, but no single word equivalent in English:

Pesamenteiro - Portuguese: one who joins groups of mourners at the home of a dead person, apparently to offer condolences but in reality is just there for the refreshments.

Hanyauku - Rukwangali, Namibia: walking on tiptoes across warm sand.

Tartle - Scottish: to hesitate when you are introducing someone whose name you can't quite remember.

Prozvonit - Czech and Slovak: to call someone's mobile from your own to leave your number in their memory without them picking it up.

Pelinti - Buli, Ghana: to move very hot food around inside one's mouth.

Biritululo - Kiriwani, Papua New Guinea: comparing yams to settle a dispute.

Poronkusema - Finnish: the distance equal to how far a reindeer can travel without a comfort break.

Shvitzer - Yiddish: someone who sweats a lot, especially a nervous seducer.

Gattara - Italian: a woman, often old and lonely, who devotes herself to stray cats.

Baffona - Italian: an attractive moustachioed woman.