I have written before about students choosing the wrong word from a dictionary or translator. Sometimes two words in their language correspond to one word in English, or one word corresponds to two.
The class was practicing ‘first conditional’. The first half of sentences were given, and the students had to write a suitable second half. One was “I’ll do the washing up if …”. The expected answer was “you cook”, but I can imagine a number of other answers which would be suitable (eg, “if you do it tomorrow”). One Korean student wrote “I theorem”. This is obviously wrong and he’d obviously chosen the wrong word from a dictionary or translator. But I wanted to find out what he’d meant, he showed me his translator and there were no other obvious words in sight, but I couldn’t guide him toward telling me anything else about this mysterious household activity. Another student from Korea was there, so I got them to talk about it briefly in Korean, but the other student couldn’t explain either.
When I got home I asked my wife about it, she said that 정리 (jeong-ni) can mean either ‘theorem’ or ‘tidy up’. Google Translate gives ‘theorem’ and ‘arrangement’, so 정리하다 means ‘arrange’. I thought about ‘theory’, which Google Translate gives as 이론, but my wife said “That’s a completely different word”. She couldn’t tell me what the difference was (explaining Korean words (her first language) in English (her second language)), but I’m not sure that I could explain the difference on the spot, either (explaining English words (my first language) and English (my first language).
I know that Pythagoras had a theorem and Darwin had a theory. Hercule Poirot might have a theory about whodunnit, but not a theorem.