I'm curious about examples. I know many languages do not have word::word translations, but a concept that cannot be translated -- even if it needs a full sentence, is a very different thing.
To understand it you must know, on a deeper level why a Swede values things being lagom, and this is surprisingly hard to put into words because it involves history, language, value systems, social patterns and even concepts like gratitude towards simple things. This word encapsulates a really big aspect of Swedish culture, making it impossible to translate accurately.