The ad market for lang=x, location=y must be abysmally small, even for tourist destinations. When you pretend that you didn't notice that the user is not a local you can still bill the impression and most importantly the occasional accidental click as a "mission accomplished".
The fraction of site visitors who are tourists may be low, but I expect it to be a segment with relatively more money that also is in the mood to spend on certain things. Looks like an audience google can charge more for.
