When you add a regular link to a page or a post, WordPress saves the URL of that page as the link. This means, if the URL changes, the link is broken.
WordPress makes it all too easy to change page addresses, causing all incoming links to go broke (404 error). Here are a few ways to do that:
Change the page’s parent
Change the slug
Change the site’s permalink structure
WPML prevents changes in URLs from breaking incoming links. When you create a link, WPML automatically makes it Sticky. Instead of storing the URL of that page (at the time the link was created), it stores the page number. This can never change, no matter what you do.
Then, when the page is displayed, WPML inserts the permalink of the page you are linking to. Whenever the URL changes all pages linking to it update immediately and will link to the correct address.