You specifically called it out as being "inaccessible" (ie, difficult to understand) to non-native speakers (of English).
Also, "a11y" looks too much like the English word "ally". That, IMO, is more likely to cause reading difficulties, particularly with non-native speakers and people with dyslexia.
I'm not saying it's difficult to understand. I'm saying it's an unwieldy word and "a11y" is easier to remember and write correctly.