I remember, there was a special version for the german market, called SimCity 3000 Deutschland. It included many german buildings.

Is this 'Addon' or special edition included in 3000 unlimited? Are there maybe even other versions available (france, england)?

Actually, SimCity 3000 Deutschland was just the German local name for Unlimited, from what I've gathered. The official blurb on the back of the boxes said "Re-create cities from around the globe with hundreds of new buildings", so it might just have it all.

http://www.mobygames.com/game/simcity-3000-unlimited

The UK Edition was the UK rename of the vanilla SimCity 3000, but I don't know if it included anything extra. The vanilla Australian release had the Opera House and the Sydney Harbour Bridge, too.

SimCity 3000 UK Edition is the UK version of Unlimited. It slightly altered the European building set to add more British style buildings and renamed other buildings to make them seem more British (Helga's Haus becomes Commuter Palace is one I found). It also includes the scenario "Liven Up Liverpool". Other than that it's the same game.

Actually, World Edition was the UK version of Unlimited, UK Edition was vanilla with a few added stuff.

On the back of the UK Edition box it says "SimCity 3000 UK Edition is based on SimCity 3000 World Edition with the addition of the UK specific building set."

Huh, guess you're right. I've sent a correction claim to my source (MobyGames).