Eunoia is a dictionary of more than 500 untranslatable (or obscurely useful) words:

sankocha: the feeling of embarrassment due to receiving an inordinate or extravagant gift, making you feel as though you need to return a favor that you can’t (Kannada)
mudita: the pleasure that comes from delighting in other people’s well-being or happiness (Sanskrit)
Erbsenzähler: literally “pea counter”: a nitpicker (German)
jayus: a joke so unfunny that one has to laugh (Indonesian)
házisárkány: “indoor dragon”: a nagging, restless spouse (Hungarian)
tretår: a third cup of coffee (Swedish)
xiao xiao: the whistling and pattering of rain or wind (Chinese)

There’s a whole subreddit for these.

(Thanks, Sharon.)