I should have said "Not being able to speak the local language isn't germane to a discussion about the Americans with Disabilities Act," because not being able to speak English isn't considered a disability under that law.
A blind person who has lost their voice could avail themselves of the text<->speech service I mentioned. If they also don't speak English they may need to employ a translation dictionary or some other translation service as well, but I'm not aware of any legal obligation for private businesses to provide translation services in the US.
