Hi @portegno
I believe you can change it by creating a Spanish translation for ACF. I think you can use Loco Translate to do it.
The other method would be using this code in your functions.php file:
function my_acf_prepare_field( $field ) {
$field['label'] = "Titulo";
return $field;
}
add_filter('acf/prepare_field/name=_post_title', 'my_acf_prepare_field');
I hope this helps 🙂