Yesterday, in my "On the monthly BetaWiki information" I suggested to have those wikis with inadequate localisation use the stable version of the MediaWiki software. This idea was because of my observation that a lot of "FYZZYING" is going on and, I associated this with the developement process.
I have had a talk with Siebrand about this and he informed me that indeed it is part of the development process. It is however also part of a process whereby existing messages are proofread and internationalised.
This changes the situation radically because this is exactly what benefits every localisation effort. It is for this reason that certainly at this stage all WMF wikis should stay on bleeding edge.