您已经提到了函数wp_title(). 在输出标题之前，它会将其值通过过滤器wp_title, 这里可以使用它来预先添加其他信息。

add_filter(\'wp_title\', \'WPSE_20181106_prepend_title\', 10, 3);
function WPSE_20181106_prepend_title($title, $sep, $seplocation) {
    // not a single post
    if (!is_singular(\'post\')) {
        return $title;
    }

    // IDs of categories that should prepend the title
    $prepend_categories = [15, 35];

    // get all categories of post
    $categories = get_the_category();
    foreach ($categories as $category) {
        // found category
        if (in_array($category->term_id, $prepend_categories)) {
            // return new format, using __() so it is translateable
            return sprintf(\'%s %s: %s\',
                __(\'Download\', \'lang-slug\'),
                $category->name,
                $title
            );
        }
    }
    // category not found, return default
    return $title;
}