Ho questo codice che mette solo la casella vuota, la spunta deve essere messa a mano, io vorrei che la spunta sia predefinita.
La stringa da modificare dovrebbe essere questa 'cookies' => '<p class="comment-form-cookies-consent">...
Codice HTML:
$req = get_option( 'require_name_email' );
$html_req = ( $req ? " required='required'" : '' );
$html5 = 'html5' === $args['format'];
$consent = empty( $commenter['comment_author_email'] ) ? '' : ' checked="checked"';
$fields = array(
'author' => '<p class="comment-form-author">' . '<label for="author">' . __( 'Name' ) . ( $req ? ' <span class="required">*</span>' : '' ) . '</label> ' .
'<input id="author" name="author" type="text" value="' . esc_attr( $commenter['comment_author'] ) . '" size="30" maxlength="245"' . $html_req . ' /></p>',
'email' => '<p class="comment-form-email"><label for="email">' . __( 'Email' ) . ( $req ? ' <span class="required">*</span>' : '' ) . '</label> ' .
'<input id="email" name="email" ' . ( $html5 ? 'type="email"' : 'type="text"' ) . ' value="' . esc_attr( $commenter['comment_author_email'] ) . '" size="30" maxlength="100" aria-describedby="email-notes"' . $html_req . ' /></p>',
'url' => '<p class="comment-form-url"><label for="url">' . __( 'Website' ) . '</label> ' .
'<input id="url" name="url" ' . ( $html5 ? 'type="url"' : 'type="text"' ) . ' value="' . esc_attr( $commenter['comment_author_url'] ) . '" size="30" maxlength="200" /></p>',
'cookies' => '<p class="comment-form-cookies-consent"><input id="wp-comment-cookies-consent" name="wp-comment-cookies-consent" type="checkbox" value="yes"' . $consent . ' />' .
'<label for="wp-comment-cookies-consent">' . __( 'Save my name, email, and website in this browser for the next time I comment.' ) . '</label></p>',