How to add 'title' attributes to breadcrumbs links?
You can use hook_menu_breadcrumb_alter().
I think it is

$item['localized_options']['attributes']['title'] = 'The title';


Play around and report here if this works!

It is called from crumbs_CurrentPageInfo::breadcrumbItems(), with some useful data with each trail item.

However, this added data is only available if Crumbs is active. Your module with the hook_menu_breadcrumb_alter() implementation may no longer work correctly if you disable Crumbs.