For the core MS fonts:

sudo apt-get install ttf-mscorefonts-installer

You may be asked to accept the license agreement, i was not asked.

They end up in /usr/share/fonts/truetype/msttcorefonts

Next is to install the clear types such as calibri

This is a bit different but can be done with the vista fonts installer script. Make sure you have the appropriate permissions.

Create a .font folder as the script needs that.

mkdir .font
wget -qO- http://plasmasturm.org/code/vistafonts-installer/vistafonts-installer | bash

All new fonts are installed in the .font folder. Now in /usr/share/fonts/truetype create folder msttvistafonts

Copy all fonts from the .fonts folder to /usr/share/fonts/truetype/msttvistafonts

*Change the ownerships to the same as that in the other fonts if needed.

If you have more fonts copy all fonts to the following folders-

/usr/share/fonts/truetype
/opt/cool/systemplate/usr/share/fonts/truetype

Run

fc-cache

Now this next command – you have to make sure that you adjust the version number to the one matching your Collabora installation for this folder: /opt/collaboraoffice Run AS ROOT (or just execute the actual command as the lool user)

su cool --shell=/bin/sh -c "coolwsd-systemplate-setup /opt/cool/systemplate /opt/collaboraoffice >/dev/null 2>&1"

And finally

fc-cache
systemctl restart coolwsd

Restart coolwsd.service and the fonts are available.

Src: https://help.nextcloud.com/t/installing-new-fonts-in-collabora/22758