There are many approaches to studying a foreign language, including the Communicative Method, stressing verbal communication with other students, or the Natural Approach, which tries to imitate the way children acquire language. When the Japanese study English, they do it with lots of grammar and translation, attempting to understand the mechanics of the language analytically, with functional use being less important than passing the all-important University Entrance Exam. While no one can accuse the Japanese of being the best linguists in the world, my students were known to teach me a thing or two about English grammar back when I was a teacher. For example, they are consciously aware of when to use ‘the’ (rhyming with ‘uh’) and ‘the’ (rhyming with ‘three’), and how words like record, present and suspect are always stressed on the first syllable if they’re nouns, but on the second when used as verbs. And ‘whom’? The Japanese have it down, even though I haven’t used the word since the third grade. Since Japanese people always expect native speakers to know every vocabulary word and bit of grammar that exists, they’re usually disappointed when we come up short.
The Japanese often know English grammar better than native speakers.