Ubuntu – Some Fonts don’t appear in LibreOffice

Fonts like Calibri and Cambria resort to using embedded bitmaps when adjusted to small sizes.

To disable this font behaviour, put the following into $HOME/.fonts.conf:

<match target="font" >
     <edit name="embeddedbitmap" mode="assign">
         <bool>false</bool>
     </edit>
</match>

Create the file if it doesn't exist.

Restart to take effect.

Sources
http://ubuntuforums.org/showthread.php?t=724818 (registration required)
http://manpages.ubuntu.com/manpages/precise/man5/fonts-conf.5.html

NOTE:
$HOME/.fonts.conf is deprecated in Ubuntu 12.10 Instead, paste the above XML code (as root) in /etc/fonts/conf.d/50-user.conf

I've found a solution for this problem. To do that you have to paste the fonts in the directory

~/.local/share/fonts

It's important to mention here that, normally, you can't see the folders which started with a dot(.)(in ubuntu folders started with . are hidden folders). To see these folders press ctrl+h or click view > show hidden files.

Now if you don't have a folder named fonts in ~/.local/share/, then create one and paste your desired fonts in that folder.

This solution worked for me; hope it can help others.