I believe you can embed the language attribute into the tag, and then write what you want the screen reader to say in the specified language: webaim designing for screen readers
I would have just made this a comment, but I don't have enough reputation points on this one, sigh.
For example, you may try something like this:
<button><span lang="es" class="sr-only">cerra</span><img src="something" alt="close" aria-alt-text="cerra"/></button>
However, I've only done a quick preliminary search to get you going in the right direction. I found this article by level access which may be exactly what you're looking for.