They may be going by the chosen language of UI. That will also include people that don't use duty finder, for example.

Of course since there are no language-specific servers like Mansion said, you will find people of all languages on all servers, let alone data centers. But hey, Europe just needs to be a pain in the ass like that. And I am from Europe, not even user of the Spanish, French or German languages that everyone caters to, so no, it's not a "nationality superiority" comment there.

Well, Europe is mostly acceptably knowledgeable in English, so that's a language you can expect to be used widely anyway as the most common one, pretty much.