Let’s not conflate middle school grades/classes in the admissions process with foreign language preparation. The OP specifically asked:
For starters, Stanford’s suggestions of high school preparation is “recommended” not “required.” An application without the “recommendations” will not be discarded. But for Stanford, and many of its peers, 3 years of foreign language equates to completed of level 3. Specifically for Stanford, I asked that exact question when I went through the process, and that was the answer they gave. So in this case, “4 years college preparation means 4 years” is an inaccurate statement.
Having said that, Stanford, and many of its peers require foreign language for graduation, so that is something the OP should take into consideration. @MYOS1634 's suggestion of taking a Subject Test to assess preparation is a good one.