Is "J" pronounced like the "je" in French?
A vocalized "sh" sound basically?
Exactly.
You realise how compact and efficient turkish is as you painstaking type the very long translation of japon degilim, Çinliyim on your phone's small keyboard
Why is (ben japonli degilim) wrong?
Because japon already means a Japanese person.
So japonlu would mean something like "someone who comes from Japanese" -- it makes no sense.
Why does Japon mean Japanese person, but Cin not Chinese person?