That aren't even yours...
http://upload.wikimedia.org/wikipedia/commons/b/bf/Kiel_Hafen_vom_CAP.jpg

As opposed to say.... The United states of America:

http://dustysneakers.files.wordpress.com/2010/03/flags-at-the-un-building.jpg

I recognise one in the OP's pic as the EU Flag... Is there some meeting going on or something?

What building is that in front of? If it has something to do with diplomacy, international relations, or multiculturalism then having a wide assortment of flags would make a lot of sense.

I don't know what the Germany pic is, but the one in America is the United Nations building. I'm assuming the one in Germany is something similar.

Texas flies six flags. And they all belong to us. Booyah.

They are preparing the foundation for their new Empire. As everyone knows, http://www.youtube.com/watch?v=hYeFcSq7Mxg

That's the UN headquarters in New York isn't it?

How do they decide which one to fly at half mast?

I don't think so. There are several flags at several different areas. Two on the left side of the river, and if you zoom in you'll see another group of the same flags on the other side of the river.

So it would have to be several international organizations, but I don't think any international organizations exist in Kiel.

I can't tell what the flags on the far right are, but the two groups on the left seem to belong to a rail station - and I'd guess off hand it is an international rail station.

I like how that picture of the beautiful German city has a McDonald's sign in it...

Americanization at it's finest.

Looking at pictures inside the Kiel Hauptbahnhof, which is in your original picture on the left, there's quite a number of different foods, particularly Asian food, and right next to the tracks down on the right is a Mediterranean restaurant (obviously Germany is not bordering this area). In fact I don't see one American fast food chain in there in a few pictures I've seen of the Hauptbahnhof, although surely there's gotta be one or two.

Multiculturalism at it's finest?

Seems like that describes the flags there.

That's a harbour. Now do some good thinking: What happens in a harbour that might just be a reason for multiple flags flowing? ^_^