Just chiming in here that if you want to tie your code to a field name instead of the ID (which would change if you created the field again elsewhere), you could change the selector in the example above to something like this:
function my_acf_ungallery_button() {
?>
<!-- Re-label ACF gallery button -->
<script>
(function($) {
window.addEventListener('DOMContentLoaded', function(){
$('.acf-field-gallery[data-name="your_field_name_here"] a.acf-gallery-add').text('Add to folder');
});
})(jQuery);
</script>
<!-- / Re-label ACF gallery button -->
<?php
}
add_action('acf/input/admin_footer', 'my_acf_ungallery_button');
