For how long has Japanese been the official language of Japan?


That is to say, in Japan, at which point in time, was it declared that
official documents had to be written in the Japanese language?

I am also looking for any additional information like where it was decided,
how was is decided, who decided that, etc...




According to the
[wikipedia](https://ja.wikipedia.org/wiki/%E6%97%A5%E6%9C%AC%E8%AA%9E), there
is no law that declares official documents should be written in Japanese, or
stating that Japanese is the official language in Japan.

But there are some laws that requires the use of Japanese is certain
situations, e.g. in court.

