Could you please have a look at my Category:Aan de slag/nl page? I created it but all links have a suffix '/nl' which looks rather ugly. Also it would look nicer if the category name could be Aan de slag instead of Aan de slag/nl.
It looks fine. We will need to do something about those old translated pages that have _(nl) suffixes, but we can't do everything at once.
The reason for the /nl suffix came out of my talks with some of the other translators. I was told that there are several languages, and the Scandinavian ones are a prime example, where there are many similarities between languages, but the often slight differences have very significant effect on grammar and therefore on meaning. In view of this we decided that all translated categories should have the language code attached, to make it absolutely clear to which language it belongs.
Another thing we should tackle, and probably sooner rather than later, is that "Pages in Dutch" should be translated ("Paginas in het Nederlands"?) Again, most of the pages listed there are old translations. When we have a new one available for each we will delete the old pages.
The aim is that in time a user will be able to set his own language when he registers (or from "My Preferences") and after that, whenever there is a suitably translated page it is shown to him automatically, instead of the English page (which is the fall-back if no translated page exists). This magic is handled by Special:myLanguage, but to use facilities such as listing all pages in a language currently is handled by lists such as "Pages in Dutch".
We are running experiments that will enable us to query pages in a language, without having to use this category, but we haven't yet got to the stage where we can make it happen automatically. It's all Work in Progress :-)