I think the closest to otsukaresama might be something like "get some rest", though I admit the original doesn't necessarily imply anything about tiredness and

I think the closest to otsukaresama might be something like "get some rest", though I admit the original doesn't necessarily imply anything about tiredness and can be used with roughly the same frequency as a greeting. Another class of untranslatable japanese words that I find interesting are onomatopoeias. The language has a ridiculous number of them! "Pikachu", for example, is a famous example that is a combination of the onomatopoeias for sparkling (pika) and a mouse's squeaking sound (chu).