Filter on widget-title does not work with custom links

Question

I added a filter to my widget titles and it looks like the filter doesn't apply on links, which are created with the links-sidebar. It does work perfectly on the blogroll or search widget

Here's a Screenshot, to illustrate what I mean.

add_filter('widget_title', 'new_title', 99);
function new_title($title) {
    $title = 'text';
    return $title;
}

I disabled all plugins and tried the same the default wordpress themes and got the same results.

Answer 1

The "Links" widget uses wp_list_bookmarks, which outputs a nested list similar to:

<li>
    <h2>[category]</h2>
    <ul class="xoxo blogroll">
         [links]
    </ul>
</li>

You can override [category] using the link_category filter:

function wpse_147543_link_category( $title ) {
    $title = 'title';
    return $title;
}

add_filter( 'link_category', 'wpse_147543_link_category' );