As mentioned already, I'm not sure if localization is the best for candidate for being held in JavaScript, but other things mentioned, e.g. single request, minified and infinitely cached JS is what I'm looking at for overall MW infrastructure - so far it's a big performance problem for MW - examples of waterfall diagram i posted for the infinite image cache also show main issue that I'm trying to attack for a while and might need more help with - there are too many JS and CSS requests are made to the server by MediaWiki: http://performance.webpagetest.org:8080/result/090218_132826127ab7f254499631... only 18th request is first image to be loaded and as you can see, JavaScript loads are blocking, meaning no parallel loading is happening.
I think it's worth investing resources into creating some process for better handling of this. Right now it's possible to cut down this configuring MediaWiki not to use user scripts and stylesheets and manually combining JS and CSS files for skin, Ajax framework and all things needed by extensons - I did quite a lot for specific installations, but it seems that it needs more systematic approach.
Good news is that MW already has some wrappers for style and script insertion that extensions use to refer to external files. It's a little bit lest fortunate with script loading sequence (e.g. it's ideal to load scripts only when the rest of the page is loaded), but that might be a much bigger challenge.
It's also worth mentioning that reducing the amount of PHP that handles JavaScript and CSS is a good idea as serving static resources is much easier then starting up fullblown PHP engine even with opcode and variable caches.
I think that there is a way to reduce the start-render delay as well as overall loading time plus, very likely to save some traffic by attacking front-end and will be happy to participate more in this.
How do we go about doing this? Can it be tied into Usability project ( http://usability.wikimedia.org/)?
Thank you,
Sergey