You don’t really need to use any package overlaying for this (and it’s not as if these fonts are ever going to be updated).
Firstly build cabextract.
wget https://www.cabextract.org.uk/cabextract-1.9.1.tar.gz
tar -xvf cabextract-1.9.1.tar.gz
cd cabextract-1.9.1
./configure --prefix=/usr/local && make
sudo make install
Then just fetch and extract all the corefonts.
mscorefonts.sh
#!/bin/bash
_sfpath="http://downloads.sourceforge.net/corefonts"
fonts=($_sfpath/andale32.exe $_sfpath/arial32.exe $_sfpath/arialb32.exe $_sfpath/comic32.exe $_sfpath/courie32.exe $_sfpath/georgi32.exe
$_sfpath/impact32.exe $_sfpath/times32.exe $_sfpath/trebuc32.exe $_sfpath/verdan32.exe $_sfpath/webdin32.exe)
for i in "${fonts[@]}"
do
wget $i
cabextract $(basename $i) -d fonts
done
To install user-wide (Flatpak will see these)
mkdir ~/.local/share/fonts
mkdir ~/.local/share/fonts/mscorefonts
cp -v fonts/*.ttf fonts/*.TTF ~/.local/share/fonts/mscorefonts/
To install system-wide (Flatpak might not see these yet)
sudo mkdir /usr/local/share/fonts/
sudo mkdir /usr/local/share/fonts/mscorefonts/
sudo cp -v fonts/*.ttf fonts/*.TTF /usr/local/share/fonts/mscorefonts/
Edit: Can I comment how much I hate the Discourse editor.