I see question marks in a box instead of letters
I don't know exactly what happened, but I'm not able to view letters in most of the applications. Chrome still works, firefox and safari doesn't work. If I go to "About This Mac" I also only see question marks in boxes. You can see it in the image. Somebody knows how to fix it? Pls let me know, thanks.
MacBook Air 13", macOS 10.14