greenthumbs,
In addition to taking more of the AP classes available at school, you might also inquire about VHS (Virtual High School) or similar courses, which many schools offer, and which can expand the AP offerings. Or asynchronous online dual enrollment classes, often available from two- or four-year state colleges at low or no cost, depending on your state and district. They won't completely address his complaints, since they are online classes, and thus won't have all the benefits of learning with in-person peers, as well as not getting him out of boring classes, but since they are asynchronous (not self-paced), it might be a way of giving him something moderately interesting to do in his down time in class (especially if teachers are aware and consenting).
With regard to advocating, you already have the world languages teacher's recommendation to skip, which will support the need for finding additional challenging curriculum prior to the end of high school. Not knowing what curricular offerings the school has, it's difficult to say what they might be able to do in-house for English, but you should be aware that there are additional AP English syllabi. One of the AP language arts sequences I've seen is AP Seminar (grade 10), AP language (grade 11), AP literature (grade 12) (or the 2nd and 3rd in the reverse order). If the school offers AP seminar next year, that might address some of his needs, as there is a fair amount of reading and writing expected, as well as discussion and often some group writing/presentation.
And fwiw, I read independently through most of my high school non-STEM classes--but usually not with my teacher's formal consent! (Actually, I read through quite a few of my university classes too...not necessarily recommending that.)
