Chinese and Japanese are certainly not the same, while Japanese does use characters derived from Chinese it also uses two other completely seperate character sets with it, in other words Japan uses two native writing systems and one Sinic-derived writing system mixed together.
Now, as to the question I'm assuming you mean Writing Systems, as alphabets do not automatically have their own distinct writing system (Engish, French and Turkish are all alphabets with the same writing system), then, well not that many more than their are now; the history of language has been such that most of the time it's been one major writing system replacing another rather than indigenous writing systems being eradicated, so for instance Turkish was originally written in Perso-Arabic but eventually was changed to being written in Latin script.