One of the interesting aspects of learning a second language for a bilingual illiterate like myself as I arrived on the shores of Japan all those years ago, is how much it teaches you about your own native language. Realising how many different meanings of "spring" there were became something of a party game and realising "this" and "this" were different words came as quite a surprise. The English language has the largest vocabulary of all apparently followed by Russian. But there are words that simply don't exist.
In Japanese, the word "genki" is a very simple example. There's no direct translation but the word means roughly "I'm feeling great", "I'm doing good". Another is "o-tsukaresama" which is called as someone leaves the office in an evening and roughly translates as "you must be tired" or "thank you for being exhausted". Not something you'd hear very often in English. And then there's "tameshigiri". The adverb to test your sword's craftmanship on another's corpse.
No longer a daily practice (as it were), it used to involve skilled swordsmen, similar to the way a car is tested by an experienced driver, slicing into the corpse in a consistent manner to eliminate the "human" element of the test. And try as I can, I really can't think of an equivalent word in the English language for that.
And as a PS as we're talking about language: Never laugh at someone's poor English, it means they speak two languages. Thank you whoever came up with that phrase.