Words that can't easily be expressed in other languages are interesting because of the way they help illuminate underlying cultural differences. Here are a few Japanese words and concepts that can't be easily translated.

Ganbatte - A very popular word in Japan that is said often and can mean anything from "Good luck" to "Try hard", to "Hang in there". Often this concept is used when encouragement is given for enduring a difficult situation.

Kondo - Literally translated as "Next time," this word can often be used just to express politeness. For example, saying "Let's go to the movie next time" would be interpreted in English as going to a movie the next time the people got together, whereas in Japanese it could mean sometime in the future or just an expression of going to a movie would be a nice idea even if there was no intention of doing so together with that person.

Ageru / Morau - Meaning "Giving" and "Receiving", the interesting thing about these words is the fact that the right one needs to be chosen depending on who is the subject of the sentence. In English you can say 'I gave her the ball" and "She gave me the ball", using the same word "gave" in both situations. In Japanese it would be more like "I gave her the ball" (using ageru) and "The ball was received from her" (using morau). In addition to just the act of giving, these verbs are often used when explaining actions that are done for another person.