One vote for the Oxford comma

Useful words which don’t exist in English

tsundoku (Japanese)

— buying a book and never reading it, possibly leaving it in a stack of other unread books

friolero (Spanish)

— a person who is especially sensitive to the cold

aware (Japanese)

— the bittersweetness which occurs during a moment of brief, transcendent beauty

age-otori (Japanese)

— to look worse after a haircut

won (Korean)

— the reluctance of a person to relinquish an illusion

prozvonit (Czech)

— to a phone a person’s cell phone only once so that they will call back (saving the originator the cost of the phone call)

H/t: Ace of Spades HQ

Phatic expressions

In linguistics, a phatic expression /ˈfætɨk/ is one whose only function is to perform a social task, as opposed to conveying information.

The 10 most difficult languages to learn