Hoi,
Many of you are actively working on the localisation of MediaWiki. In the last couple of days I blogged twice on possible maintenance jobs on your local wiki. 

There are two parts to it:
The bottom line is that messages available at translatewiki.net will be available on any Wiki. This is why you want to always localise at translatewiki. When messages exist that are the same on your wiki and on translatewiki they may cause problems in the future. This is why localising locally is typically not the thing to do.

In the post a Toolserver tool is mentioned that makes it relatively easy to do all this. 
Thanks.
      Gerard

http://ultimategerardm.blogspot.com/2012/02/cleaning-up-mediawiki-namespace.html
http://ultimategerardm.blogspot.com/2012/02/cleaning-up-mediawiki-namespace-ii.html

http://toolserver.org/~robin/?tool=cleanuplocalmsgs