Unfortunately, we don't have a definite answer for this. You can get a pretty good idea yourself by comparing international domains, e.g. YouTube.com or Wikipedia.org, in the research area for different search engines, e.g. Google.fr and Google.uk, or, if possible, the country domain directly, e.g. Amazon.fr and Amazon.uk. Based on the number of longtail keywords, you can compare the relationship between the countries and which country has more or less keywords being monitored.