If you ever get {#advanced_dlg.link_url} (and similar values, such as {#advanced_dlg.link_list}, {#advanced_dlg.link_target} or {#advanced_dlg.link_titlefield}) in your advanced theme link window in TinyMCE, the language file has not been loaded properly. The two simplest reasons for this is that the language file may be missing completely, or that you’ve provided a language key that does not exist. To check for the first issue, check that you have en_dlg.js in your themes/advanced/langs/ directory. To check for the other issue, try to set the language parameter (when creatinging the TinyMCE object) to ‘en‘ just to test it with the default value. If it works with ‘en’, you’re probably missing the local translation file for the advanced theme. Get it from the TinyMCE site and live happily ever after!