i have already read about this topic, but this not the problem on my site.
I have used all the years the “-” sign without problems. Now after changinge to GPP and local fonts, this sign is displayed as a double minus. So two of this signs in series. There must be a reason for that, no?
GP/GPP itself has no control over your content like this. It’s possible that the font you switched to makes the double dashes more apparent.
WordPress runs filters on your content and converts some characters. Things like curly quotes, em-dashes (double dashes) etc.. are added by them. Adding the filters I linked to will tell WordPress to stop converting those characters.