...I've only ever seen Fritz-Kola as a Berlin phenomenon tbh. There are some other regional brands though (e.g. in the Eastern German parts you're likely to see Vita Cola next to Coca Cola - completely different taste though).
Hamburg is also full of Fritz Kola. As this article[1] claims, Fritz Kola is the third largest cola brand in Germany. And it is exported in over 20 countries. They also search for bottling plants in Spain to produce drinks over there.
I've seen it for sale in at least a couple of bars in Copenhagen.
A bar owner I know here says selling these more-premium sodas is a good way to make a bit of extra money on people who aren't buying alcohol — you can charge more for Fritz-Kola than for Coca-Cola.
A different bar owner I know chose Jolly Cola, avoiding an American product but keeping a low price.
