Searching german forum

Hi,
when I’m searching for a problem, I would like (first) to do a search in the german forum.
Therefore I go to https://forums.opensuse.org/forum.php and select “deutsch/german”.
It appears the german forum.
If I than write my question into the input box,on the top, on the right side I get answers from the english forums too.
It depends on the words typed in. If the words are similar in english and german (like USB) I get the answers mixed from different forums.
If I use a german word like “Festplatte” it makes no sense to search in english forums.

Somewhere I found, that I have to select “search in subscribed forums”.
This I found in advanced search with “search single content type” and “search type = posts” selected.
In additional options I can select “Search subscribed forums”.
Doing this I get the message

You are not subscribed to any forums

But I didn’t find anything about subscribing forums.
I have already searched all FAQs, forum rules etc.
I would like to select the scope for the search.
For me it’s very mysterious how to do an optimized search…

When you go to a forum e.g. from the home page > German > Anwendungen there is just below the main title and before the list of threads starts the menu Forum Optionen. There is an item Dieses Forum abonnieren.

OK, now I found it. Thank you.
But doing so, I subscribe to a sub-forum.
This is not what I wanted to have and it seems not very sophisticated.
I want to subscribe to a whole (main) forum, because most times I cannot locate the sub-forum for the search.
Although the forum has only 5 subforums. I can do it.

Sometimes I’m not logged in!
Do you know the search route then?

Apparently it only allows you to subscribe to those forums individualy (which seems to incorporate subforums of this like in Desktop).

And when you are not loged in, the forums can of course not use information that is bound to your username.