Hello everyone,
I have noticed for some time that the texts here in the forum looked strange and the special characters were not displayed and I have now also found out what the reason is:
If you set the forum language to English in the user profile, the encoding ISO-8859-1 is used, which means that the text cannot be displayed correctly:

As soon as Polish is set again, IS0-8859-2 is used:

I think it makes sense to use ISO-8859-2 for English as well.