I'm rather shocked to find the wordpress user interface in German now. Yes, I blog in German, but I would definitely prefer to have all the buttons and links in English since I am used to it. Besides, what I have seen so far, some of the German translations are not really satisfactory and inconsistent, to say the least.
(I tried to find and correct mistakes via http://translate.wordpress.com but to no avail.)
In the profile section, you can select the primary language of the blog. I suppose if I switched to English, I would get the English user interface back but that would not be a sensible workaround in my eyes. There is also a remark that it will be possible to change the language of the user interface in the future.
However, wouldn't it be better to adapt the interface language to the blog language once the language selection feature has been rolled out? My suggestion would be to keep the English version till then since all users are familiar with it. In fact, it is not so easy to get used to the changed interface even if it's in your native language...
I'll send in feedback about this.