I am logged in to Stack Overflow (in English) from a Spanish-speaking country and see an advert for the Spanish language version of Stack Overflow. The advert, when translated, reads "if you're tired of English, learn and share in Spanish".
The odd thing about it is that this advert URL looks something like
https://googleads.g.doubleclick.net/pcs/click?.......&adurl=http://es.stackoverflow.com:80.... implying that the Stack Exchange network is paying Google for clicks on an advert which appears on one of their own sites that they control - they will obviously get some money back by allowing Google to display ads, but equally obviously this will be less than the advert is costing.
If they want to run that sort of advert, wouldn't it be more cost-effective to detect for themselves that the client IP address is in a country where the main language is from a different site in the Stack Exchange network, and in that case, put up the advert themselves and cut out Google?
The wording of the advert (see my translation above) is such that it only makes sense for it to appear on the English Stack Overflow site, not any third-party sites, which makes this doubly odd.
Or do they have some kind of weird tracking arrangement with Google? (There were a lot of numeric IDs in the above URL, which I stripped.)