Random memory
At school, I taught my Japanese girlfriend (part of) the Korean alphabet and we used it to write notes to one another in Japanese.
I imagine that very few people at school, if any, would have been able to understand those notes: the Koreans could read but not understand them, and the Japanese couldn't read them. (On the other hand, if a Korean read it out loud to a Japanese, then they could arrive at the meaning of the note.)
The Korean alphabet lends itself surprisingly well to Japanese, I found; the main obstacle was a missing letter for /z/.
