Has anybody studied, seen a study or even just gathered anecdotal knowledge about which type of affordance works best for switching between languages on a website. My guess would be that spelling the name of the language out in that language would be the most obvious. ...but I've seen a drop-down used that says "English" by default, I've also seen links that say "language" ..etc.
There are some common rules for this.
You should always spell the name of the language in it's native form.
E.g. "Deutsch" for German.
One good test is to switch to Chinese and if you can still find the language switcher you're on a good way. Imagine if they would have written German in Chinese letters. You could never find it. A world symbol is also a fairly well understood symbol for the language switcher.
The blog globalbydesign covers this topic fairly well.
I got the book also, it does not have too much content, but it's fair for the price.
I wrote a blog post that specifically covers the language switcher topic: