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I have a US site that receives traffic from many countries in Europe and I now know most of these countries are not served ads. The preview tools states 'no ads available' for many countries and this explains the low or non existant CTR.
France is one in particular not showing ads, if I host a French version of my site, will ads show?
>Added: I also notice that sites that have been running Adsense for a long time seem to have pretty good ads for European countries. Maybe it takes some time for additional countries to be added?