I don’t know if it has been discussed in this forum. I can see that Google’s SERPS can be different for the same keywords when you search on different Google’s portals and the language of the portals are different too. For example, my website is written in spanish and it includes an article about an american author. When you search “name lastname” of that author on google.com (English) my article appears in the second page of SERPS. When you search on google.es (Spanish), or another portal in Spanish, my article is on the first page on SERPS, in the second position. When you search on google.jp (Japanese) my article is again on the first page, but in a bit lower position.