Filter translations (gettext strings) on specific admin pages

According with the codex, get_current_screen() has to be used later than admin_init hook. After a few tests, it seems that the safiest way is to use current_screen action hook instead of get_current_screen():

add_action('current_screen', 'current_screen_callback');
function current_screen_callback($screen) {
    if( is_object($screen) && $screen->post_type == 'mycpt' ) {
        add_filter( 'gettext', 'theme_change_comments_label', 99, 3 );
    }
}

function theme_change_comments_label( $translated_text, $untranslated_text, $domain ) {

    if( stripos( $untranslated_text, 'comment' ) !== FALSE ) {
        $translated_text = str_ireplace( 'Comment', 'Review', $untranslated_text ) ;
    }

    return $translated_text;

}

You can reuse the filter if you want, for example in the frontend for “mycpt” archives:

add_action('init', function() {
    if( is_post_type_archive( 'mycpt' ) ) {
        add_filter( 'gettext', 'theme_change_comments_label', 99, 3 );
    }
});