I assume that the reader is familiar with the "SEO friendly URLs" concept. If not you can start reading these:
At the cost of beating my own drum, I will consider a real case: http://wildzone.it. It is an image gallery where the contents are organized in a structure like this:
LANGUAGE -> CATEGORY -> GALLERY -> IMAGE
So the smartest way to write the URLs would be: http://wildzone.it/en/italy-4/seaside-of-sardinia-19/orosei-117f.html (external URL). The internal URL, actually managed by the cms and more concise, is: http://wildzone.it?l=en&cat=4&gal=19&id=117. As you can see, the external URL is SEO and user friendly. It embeds the id number of the language/category/gallery/photo. In addition, reading the URL gives the user an understanding of the site's topic and organization.