The interface font is a monospace one:
http://i.imgur.com/MXdGFip.png
There is no way in Settings to change this. Monospace fonts should only be used for code and code-like text, not for everything.
A safe default user interface font for Linux systems is "sans", which will default to whichever sans-serif font the user has set up on their system, typically DejaVu Sans.
I see this in the console:
Code: Select all
Fontconfig error: line 29279311: syntax error
Fontconfig error: Cannot load default config file