I’m not sure if you are still looking for a solution for this, but I ran into a similar issue trying to add alt tags / tooltips for icons.
In the end, I assigned a class to the items, and used jQuery to add an “aria-label” attribute for screen readers and a “title” attribute for the tooltip on hover.
Below is the jQuery I used for my particular situation:
jQuery(document).ready(function($) {
$('.feature_food_onsite').attr('aria-label', 'Food Onsite');
$('.feature_food_onsite').attr('title', 'Food Onsite');
$('.feature_family_friendly').attr('aria-label', 'Family / Child Friendly');
$('.feature_family_friendly').attr('title', 'Family / Child Friendly');
$('.feature_pet_friendly').attr('aria-label', 'Pet Friendly');
$('.feature_pet_friendly').attr('title', 'Pet Friendly');
});
Hope that helps.