Is there any way to display the link of a WordPress page without relying in its slug (or full path)?

From what I understand, you want a URL to your page, that will work even if you change the page slug?

You can do this by linking to the default permalink for that particular page, for example http://localhost/taiwantalk2/?page_id=139.

This URL will always work even if your permalinks are updated. WordPress handles the redirects for you.