Accessing via common or garden browser
The csi18n service can be accessed using commonly available browsers.
Your browser will need to be modified to emit the Accept-Language HTTP header you prefer. Here's the W3C's general page on this subject. Notice that apart from IE, custom languages (such as 'klingon') don't seem to be directly accessible: Firefox, for example, requires you to manually edit within about:config.
Once done, you might visit David Grove's request headers page to get an independent idea of what your browser is sending.