When you compare these statistics with statistics about Wikipedia, they are essentially different. We share the notion that our community is what is most precious in our project but for us it is important to have people who come regularly to our project to work on a finite amount of work for them.
The group statistics tell the story best for MediaWiki; some languages are 100% localised and you will notice from the screen shot that this is achievable for every language big and small.
I received a graph from Dedalus that shows a correlation between the number of articles and the quality of the localisation. In essence all Wikipedias over a certain size are completely localised. It makes sense because how can you appreciate what you are asked to do otherwise?
Horizontally you find the number of articles in a logorithmic scale and vertically the percentage of localised messages. A subset of 54 languages is used. Languages with over 100.000 articles are fully localised.