Honestly, I hadn’t given much thought to icon fonts as they relate to accessibility until flipping through Death to Icon Fonts today. By the way, I wish there was a video of Seren Davies’s presentation, but I can’t seem to find one. She points out that people using alternative fonts and screen readers might not be getting a very good experience when icon fonts are used. Her recommendation is to use SVG instead, which has a few other advantages.
Given the lack of accessibility, it might be worth reconsidering the use of icon fonts. Choosing not to use icon fonts might be easy on a new project, but what if you already use them? Filament Group offers some detailed advice on bulletproofing accessible icon fonts that might be a good start.