You didn't ask about Australia, but it has https://forums.whirlpool.net.au/

It predates HN and always has always been the place the best technical people in Australia butt heads. Their problem is they aren't up to the same standard as here - where you have the best technical people in the world butting heads.

For Germany, Heise online maybe, www.heise.de

But that would be a very big "maybe", because it is very different in all aspects.

That is the German alternative, not the European alternative.

If you can understand German, that is.

For the Netherlands probably Tweakers.net.