There was a little book a few years ago (it's out of print now) called "Ai: Japan Through John Lennon's Eyes: A Personal Sketchbook" that was a little sketchbook/language aid that John had created for himself when they were in Japan.
I found some info about it on Amazon, there was one customer review:
This book is the only English picture book that introduces Japanese that I have ever seen. John's sketches show his understanding of the Japanese language well. What also makes the book special is John's position in Japanese life. He learned Japanese as a foreigner looking at Japan.
Reading it will be a source of enjoyment for everybody whether beginner or advanced in Japanese.
Thank you John for such a wonderful expression of Ai.
I have a copy, and it's sweet -- you might want to see if you can find a copy on eBay or in a used bookstore or something, it'll give you an idea of how John was attempting to learn Japanese.