Maybe there are reasons for that:

Google Translate is based on English, so it translates best into languages which are related to English (like German, French, Russian, Scandinavian languages etc).
Even for these closely related languages, Google employed trained translators to translate and evaluate lots of strings (I happen to know a translator who was employed for Norwegian).

Fwiw,

Oliver (aka BT)

From: wikimediake-bounces@lists.wikimedia.org [mailto:wikimediake-bounces@lists.wikimedia.org] On Behalf Of Abbas Mahmood
Sent: 22 April 2011 21:09
To: The discussion list for the upcoming Wikimedia Kenya chapter.
Subject: Re: [Wikimedia Kenya] WikiSaturday

In other languages, Google Translate seems to be working fairly well. Google Kenya has alot of work to do with Swahili, though...

Date: Fri, 22 Apr 2011 09:46:40 +0300
From: wanjaustev@gmail.com
To: oliver_stegen@sil.org; wikimediake@lists.wikimedia.org
Subject: Re: [Wikimedia Kenya] WikiSaturday

Hi,

I cannot understand anything.It looks to me like just an arrangement of words!!

SOMETHING NEEDS TO BE DONE.

REGARDS,

2011/4/22 Oliver Stegen <oliver_stegen@sil.org>

PS: To those of you who’re still convinced of Google translator’s effectiveness when it comes to translating between English and Swahili; just look at its translation of my first paragraph and decide for yourself how much you understand (and whether you’d want such a translation in Wikipedia):

Nina J'mosi something about the Wikipedia. Mkichangia articles Kiswahili (http://sw.wikipedia.org) Do not use while the translation of Google (http://translate.google.com/toolkit/) indiscriminately. First you must ensure that the target article ijaandikwa yet. If not you can delete the information that zimeshaingizwa another. So it did e.g. just yesterday with an article of author Marjorie Oludhe Macgoye Kenya, look here: http://sw.wikipedia.org/w/index.php?title=Marjorie_Oludhe_Macgoye&diff=next&oldid=545629
It is true, in part a translation of the Google of yesterday had improved article on November 16, 2010 except for the greater part was badly affect, eg [[Category]] zilirudishwa all the [[Category]], and "category" false and also a link to [[fi:]] kilifutwa and many other things. Do not do it. It is the use of such distraction that our old wikipedia yamemkasirisha Pala. He is a "bureaucrat" to rely so often help. Msimkasirishe. Thank you!

Thanks!

Oliver (aka BT)

<snip>