There are a number of ways to install fonts on Ubuntu. Here’s one really simple way.
First, download or gather all the Thaana fonts which you want to install and put them all into a folder on your desktop.
Then, press Alt+F2, enter the following command inside the Run dialog box that appears and click Run.
gksu nautilus /usr/share/fonts/truetype
This will open a window on your desktop. Now cut the folder with the Thaana fonts and paste inside this window.
After that close the window, press Alt+F2 one more time and paste the following command in the box that appears. Before you click Run this time, make sure you tick the “Run in terminal” checkbox.
sudo fc-cache -f -v
This will open a new Terminal window and you can see the caching process. One this process ends, the window will close automatically. Your Thaana fonts will now be installed. You can use this method to install other types of fonts as well.