@Pavel Create and cd into a directory of your choice (e.g., /opt/mathematica/fontconfig), do rpm2cpio https://rpmfind.net/linux/fedora/linux/updates/28/Everything/x86_64/Packages/f/fontconfig-2.13.0-5.fc28.x86_64.rpm | cpio -idm, then prepend LD_LIBRARY_PATH=/opt/mathematica/fontconfig/usr/lib64 to the executable in your Mathematica.desktop file.