I think the disability office is not following up because it is not a problem sizzling on the desk of the person the OP has been dealing with. Several alternatives have been suggested, like video taping the speeches, taking an online course, or taking the course at another school and transferring the credits in. I think it may be easier to work directly with the professor at the BEGINNING of the course about the speeches and doing them privately or on video, or having alternative projects, rather than expecting the disabilities office to be a go between. I’d go to the dean of arts and sciences ask for help? Ask what they do for deaf students, or those who are physically mute and unable to do a speech (that other can understand), or students who speak little English.
The state may require that the course be taken but it doesn’t restrict the professor as to what can count for completing the course. Is a pass/fail option available? What can substitute for the final speech? Have a list of courses that may work for substitution. If the dean sees that your son is trying to complete the course, I bet he’ll be more helpful and trying to figure out a way to complete it.
You can file a complaint but that may take a long time to resolve.