On steam unfortunately ET is blocked in germany.
But why?
It's a free game and it is possible to legally download the game on so many german websites. I really Don't understand that decision. :(

There are symbols from WWII in game, that are banned in Germany (whole game is banned). They don't like their history :P

Oh damn, is that what's going on? i was going through here trying to figure out why it didn't download, let's see what a VPN can do here

after you get it on steam, or if you won't manage, get ETLEGACY anyway, it makes the game better and much easier to join populated servers. Better graphic settings etc.
Download it, then play it, as simple as that. If you manage to get the game on steam, put the whole thing in your game's folder (steam version game) then remove et.exe and rename etl.exe to et.exe
Now when you run via steam it'll launch the Etlegacy version.
https://www.etlegacy.com/
here's the download.

Follow-up: i used ExpressVPN to connect to a dutch server, restarted steam, and could get it.

There are symbols from WWII in game, that are banned in Germany (whole game is banned). They don't like their history :P
Enemy Territory doesn't feature swastikas or SS runes, and is available in Germany outside Steam. This is a move by Steam or Bethesda, not German authorities.

Swastikas are not generally prohibited in video games in Germany. It rather depends on the content and their use in the game whether one glorifies or trivializes Nazism. And whether you play on the side of the anti-fascists or on the side of the Nazis. In this case Wolfenstein ET should be fine.