Apocryphal or not, there is a story from the early days of machine translation. The machine was laboriously programmed for English to Russian translation. After basic checks, they decided to try a fairly difficult sentence, so they keyed in "The spirit is willing but the flesh is weak". and in a few seconds the TTY terminal chattered out "Водка отличная, но мясо гнилое": The Vodka is excellent but the meat is rotten".

Back then, machine translators were more of expert systems based on large amounts of preprogrammed data and decision trees. They didn't yet have the heuristic machine learning algorithms as they do now. It's still a work in progress. Just this morning I asked Google to translate "Cool, man!" in Bengali, and the output was roughly "Calm, human!"

This truly demonstrates the deep and obscure difficulties in natural language processing. Such things are by no means obvious until they jump out at us from nowhere. We have come a long way in the short time since the inception of AI, but there is still a long way ahead. If anything, it teaches us to respect the fantastic but little understood powers of the human mind.