When I was learning English, it was really hard trying to figure out which ending 的 became. Usually but not always it was -al, sometimes it was -ific.
And now my English is decent and my Japanese is rusty, so yeah, the human brain can only be stretched so far.
I'm headed back to Japan in January, and it's gonna be so weird hearing 日本語上手, it's gonna feel like a slap every time.