Based on the first proposition posted by @Mx. (posted sept.15th 2014) I created a variant to get a decent HTML markup for ARIA support.
$('.slideshow').slick({
slide: 'img',
autoplay: true,
dots: true,
dotsClass: 'custom_paging',
customPaging: function (slider, i) {
//FYI just have a look at the object to find available information
//press f12 to access the console in most browsers
//you could also debug or look in the source
console.log(slider);
var slideNumber = (i + 1),
totalSlides = slider.slideCount;
return '<a class="custom-dot" role="button" title="' + slideNumber + ' of ' + totalSlides + '"><span class="string">' + slideNumber + '</span></a>';
}
});