In the niche that I'm in, the generic phrases are bidding at $10-$15 or higher for the top spot. When I search for the french or spanish equivalents, there's nary an ad to be found (a couple folks from brazil/france). Have I found an untapped area? Or is there a reason there are no ads there?
Although, the largest barrier seems to be that the web devs, marketers, etc, only speak one language and while translation services are available, when you want to just change some ad copy on the fly, or read over your stats, it's much more difficult when you have no idea what the keywords are.
I'm suspecting eWhipser is correct about English-centric businesses. However my clients have indicated that they would consider hiring alternate language staff. And in this industry, if I get a few hundreds of clicks per month it's worth doing that.