Some thoughts on design...

To better accommodate varying abilities of a client community, it’s important to explore design with a holistic approach. Consider the complexities of a single person, and then widen the lens to a group of people—and it becomes apparent that the research required to fully understand a client community will come from various disciplines and departments of thought. A starting list could be comprised of the following: Public Health, Cultural Anthropology, Anatomy, Linguistics and Psychology.
From here, a diverse and relevant team of specialists in these areas can be assembled to observe, communicate with and comprehend the client community (along with the designer of course). This recommendation is rooted in the idea that all humans are dynamic and unique, and that no one design “solution” can appropriately serve all people.