(cc'd to mediawiki-i18n mailing list too)
In r30349, Raymond fixed bug 10365 (https://bugzilla.wikimedia.org/show_bug.cgi?id=10365), allowing Special:Version to be localized. However, I am not sure how smart an idea that was, since nowadays almost every extension has a description message. Why so?
Firstly, let's have a look at WikiTextLoggedInOut extension (http://svn.wikimedia.org/viewvc/mediawiki/trunk/extensions/WikiTextLoggedInOut/). It is a simple parser hook extension from Wikia I added on 30th of June to the SVN repository. It adds two parser hooks that show different output to the user depending on his/her login status. How simple is that? Well, it has a description message too. It is a simple parser hook tag that does not need i18n at all, unlike special page extensions and such do.
Secondly, some extensions, such as the above-mentioned WikiTextLoggedInOut have only one message... the description message. Now, with the i18n file being added, the extension's i18n gets loaded on every pageload if the page has the extension tag. I am relatively sure that it slows things down. Maybe only a few milliseconds, but the point is that it can be avoided.
Thirdly, what if the original developer wants or needs to change the extension description, upon adding or removing some features? That's right, some languages would see old messages with incorrect information while some other languages might have correct info. And users might end up trying to use a removed feature, which would obviously cause them frustration. After all, you cannot demand that volunteer translators do translations 24 hours per day. In fact, we already have several developers continuously working on i18n, desperately trying to keep them in sync - resources that would be much better spent on developing new functionality and fixing bugs.
I have heard an interesting argument in favor of description messages: that they allow the wiki users to know what features are installed and what they can use. Now, I don't think that's true. The local help pages are for documentation and so are the extension pages on MediaWiki.org. If something should be done, the local admins/sysadmins should create a help page about the feature or announce it and maybe point the users to MediaWiki.org for more information if they don't create a help page or such.
I have spoken to several fellow MediaWiki / extension developers, some native English speakers and some are not, but most of them seem to agree that the localization of Special:Version is "i18n gone bad". I have to agree with them, as description messages do not provide anything useful for users or developers - having, for example, the words "MWSearch plugin" in 39 different languages (http://svn.wikimedia.org/viewvc/mediawiki/trunk/extensions/MWSearch/MWSearch.i18n.php?revision=36271&view=markup) is probably one of the most pathological examples. These extension description messages just cause extra stress for MediaWiki and the servers running MediaWiki. In the past, you could always find at least one English page on the wiki, no matter what its content language was - Special:Version. Now you have to add ?uselang=en to see the 'correct' version of the page.
Another interesting and related point is the addition of core 'blank' page in r36856 (http://svn.wikimedia.org/viewvc/mediawiki?view=rev&revision=36856) by Domas. He added the blank special page as a baseline to profile startup times. He used to use Special:Version for profiling, but since it's overloaded with useless i18n crap now, it is no longer effective.
If there is something that should be translated in Special:Version, it most certainly is not extension descriptions. It is the license text. And to avoid legal issues, it should have a hardcoded English string, for example, "The English version of the license can be found here" or something. As a user, I would like to know my legal rights rather than of what parts the software is made of.
I believe that the description message / localization of Special:Version does more harm than it does good, plus it is pointless (as Rob Church correctly pointed out in his initial reaction: https://bugzilla.wikimedia.org/show_bug.cgi?id=10365#c1). I would request that this would be removed from core.