Modify the display Text of number of comments

Replace the

<?php
        printf( _nx( 'One comment:', '%1$s Reviews:', get_comments_number(), 'comments title', 'simone' ),
           number_format_i18n( get_comments_number() )
                 );
?>

with

<?php 
    do_action('my_comments_title_hook');
?>

And then ( since the function comments_template() is called within the loop, you can simply ignore the post type check using $post->ID ):

function change_coments_title() {

    if ( get_post_type() == 'post' ) {
        printf( _nx( 'One comment:', '%1$s Comments:', get_comments_number(), 'comments title', 'simone' ), number_format_i18n( get_comments_number() ) );
    } elseif ( get_post_type() == 'review' ) {
        printf( _nx( 'One Review:', '%1$s Reviews:', get_comments_number(), 'comments title', 'simone' ), number_format_i18n( get_comments_number() ) );
    } elseif ( get_post_type() == 'page' ) {
        printf( _nx( 'One Review:', '%1$s Reviews:', get_comments_number(), 'comments title', 'simone' ), number_format_i18n( get_comments_number() ) );
    }
    //Other post types
}
add_action( 'my_comments_title_hook', 'change_coments_title' );

The example function above doesn’t change anything for ‘posts’, but if you are on a CPT called ‘reviews’, it will do the trick. Do let me know if you want to chenage the title for all post types.