好的，这就是我所做的：首先，我复制了类/类219个svg图标。php到子主题。重命名为class-mytheme-svg-icons.php.

添加了扩展New_SVG_Icons 类别：

class New_SVG_Icons extends TwentyNineteen_SVG_Icons {

    /**
     * Gets the SVG code for a given icon.
     */
    public static function get_svg( $group, $icon, $size ) {
        if ( \'ui\' == $group ) {
            $arr = self::$ui_icons;
        } elseif ( \'social\' == $group ) {
            $arr = self::$social_icons;
        } else {
            $arr = array();
        }
        if ( array_key_exists( $icon, $arr ) ) {
            $repl = sprintf( \'<svg class="svg-icon" width="%d" height="%d" aria-hidden="true" role="img" focusable="false" \', $size, $size );
            $svg  = preg_replace( \'/^<svg /\', $repl, trim( $arr[ $icon ] ) ); // Add extra attributes to SVG code.
            $svg  = preg_replace( "/([\\n\\t]+)/", \' \', $svg ); // Remove newlines & tabs.
            $svg  = preg_replace( \'/>\\s*</\', \'><\', $svg ); // Remove white space between SVG tags.
            return $svg;
        }
        return null;
    }

    /**
     * User Interface icons – svg sources.
     *
     * @var array
     */
    static $ui_icons = array(
        \'new_drop_down_ellipsis\' => /* custom – ao_drop_down_ellipsis */ \'
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
    <path fill="none" d="M0 0h24v24H0V0z"/>
    <path d="M2 2v20h20V2H2zm4 12c-1.1 0-2-.9-2-2s.9-2 2-2 2 .9 2 2-.9 2-2 2zm6 0c-1.1 0-2-.9-2-2s.9-2 2-2 2 .9 2 2-.9 2-2 2zm6 0c-1.1 0-2-.9-2-2s.9-2 2-2 2 .9 2 2-.9 2-2 2z"/>
</svg>\',

    );
}

返回函数。子主题的php我添加了复制文件的路径：

function include_extra_svg() {
    require_once get_theme_file_path( \'classes/class-mytheme-svg-icons.php\' );
}
add_action( \'wp_enqueue_scripts\', \'include_extra_svg\' );

然后，我在之前的函数和类上引用了该函数和类：

function replace_ellipses() {
    if ( function_exists(\'twentynineteen_add_ellipses_to_nav\') ) {
        remove_filter( \'wp_nav_menu\', \'twentynineteen_add_ellipses_to_nav\', 10, 2 );
    }
    function twentynineteen_add_new_ellipses_to_nav( $nav_menu, $args ) {

        function mytheme_get_icon_svg( $icon, $size = 24 ) {
            return New_SVG_Icons::get_svg( \'ui\', $icon, $size );
        }

        if ( \'menu-1\' === $args->theme_location ) :

            $nav_menu .= \'<div class="main-menu-more">\';
            $nav_menu .= \'<ul class="main-menu">\';
            $nav_menu .= \'<li class="menu-item menu-item-has-children">\';
            $nav_menu .= \'<button class="submenu-expand main-menu-more-toggle is-empty" tabindex="-1" aria-label="More" aria-haspopup="true" aria-expanded="false">\';
            $nav_menu .= \'<span class="screen-reader-text">\' . esc_html__( \'More\', \'twentynineteen\' ) . \'</span>\';
            $nav_menu .= mytheme_get_icon_svg( \'ao_drop_down_ellipsis\' );
            $nav_menu .= \'</button>\';
            $nav_menu .= \'<ul class="sub-menu hidden-links">\';
            $nav_menu .= \'<li id="menu-item--1" class="mobile-parent-nav-menu-item menu-item--1">\';
            $nav_menu .= \'<button class="menu-item-link-return">\';
            $nav_menu .= twentynineteen_get_icon_svg( \'chevron_left\' );
            $nav_menu .= esc_html__( \'Back\', \'twentynineteen\' );
            $nav_menu .= \'</button>\';
            $nav_menu .= \'</li>\';
            $nav_menu .= \'</ul>\';
            $nav_menu .= \'</li>\';
            $nav_menu .= \'</ul>\';
            $nav_menu .= \'</div>\';

        endif;

        return $nav_menu;
    }
    add_filter( \'wp_nav_menu\', \'twentynineteen_add_new_ellipses_to_nav\', 10, 2 );
}
add_action( \'wp_enqueue_scripts\', \'replace_ellipses\', 0 );

瞧！我不确定这是否是最好的方法，但它确实有效。