This answer addresses the ttf-mscorefonts-installer 'half-installed' error. This error can occur because Microsoft True Type Core Fonts for the web, which is installed by the ttf-mscorefonts-installer, is Microsoft proprietary software, and although it can be installed free of charge, it cannot be installed without accepting the Microsoft End User License Agreement (EULA). The problem is that the Microsoft EULA window pops up behind the Ubuntu Software Center window, and since it is smaller than the Ubuntu Software Center window, it is often completely covered up so that it can't be seen. Then when you close the Ubuntu Software Center window, it also closes the EULA window, resulting in the ttf-mscorefonts-installer package being 'half-installed'.
If this happened to you, then you have to uninstall the ttf-mscorefonts-installer package and reinstall it, preferably from the terminal, so that the EULA window won't have any big windows to hide behind.
Run sudo apt install ttf-mscorefonts-installer
and accept the EULA, or else if you already have ttf-mscorefonts-installer installed and you didn't accept the EULA, then uninstall ttf-mscorefonts-installer and reinstall it like this:
sudo dpkg -P ttf-mscorefonts-installer
sudo apt install ttf-mscorefonts-installer
Use the Tab and Enter keys to accept the EULA in the Microsoft TrueType core fonts window that pops up. The terminal will output a new message each time it finishes downloading a new font. Wait a bit until the terminal tells you that it's finished downloading and installing the Microsoft TrueType core fonts.
If this method doesn't work, then download the latest version of ttf-mscorefonts-installer and double-click it to install it using the Ubuntu Software Center.