So I live in Switzerland for a few years now but sorry my german is not that good so I will reply in english.

As far as I know the most active German speaking server is Shiva so it would make sense that Swiss could gather there from the German speaking regions. But I dont think there is a specific server for where most Swiss are. Generally most europeans are scattered around as they just put into a random server when they begin.

But there are yearly game convention in Switzerland if you wanna meet up some fellow folks