ThomasB - 7:20 pm on Jan 9, 2009 (gmt 0)

Being based in Germany and German I'm even surprised that the CTR is 1/2 of your normal CTR if there is competition in that field. I've tested quite a bit of stuff over the years and usually suggest the following scenario for targeting the German audience:
- If you have a German website, make German ads
- If you have an English site, make English ads

The reason is usually quite simple, even though you might increase the CTR with German ads your conversion rate will be very, very low as you don't show what people expect - German content. On the other hand if you already pre-selected English speakers you have a higher chance of converting them on your English site as this is what they expect to see after the click. So never forget that a click hardly ever is a conversion. :-)