Applying for a visa before graduating HS

Okay so, for context, I am thinking about enrolling into a language school in Japan in April of the following year. However, I won't be graduating high school till December of this current year. You obviously need to have completed 12 years of education to get a student visa, right? And it usually takes about 6 months from start to finish to receive one. If I wanted to do everything on time, I would seemingly have to apply during November or December, yet I would *probably* not have my high school diploma during that time, at least until a certain day in December. That is why I'm asking if it is still possible to apply for a visa despite this.
Would I still be able to apply to a school? Or would it be too risky or be too much of an issue? Should I just wait until the next term?

I am looking forward to your replies, thank you very much!

As you are aware of, the school enrollment and visa application process takes quite some time, so it should be OK if your current school can issue you a paper saying that you are �gexpected�h to graduate high school by certain date/month, and another paper certifying that you indeed are studying currently there.
But better check with the specific school you will be applying with.

Thank you, will do ^^
Let�fs hope it�fll all turn out well.