Which version of Protege are you using (you can copy-paste the
"Protege" and "Platform" sections from the console, or at least get
the version number from the Help -> About
menu)? On what operating system?
What language packages are installed on your OS? What is the
Does the ontology contain labels in different languages? Would it be
possible to share the ontology with us, perhaps?
What do you see in the "Set Language:" preferences if you open the File -> Preferences... menu, select
the Renderer tab and click on the Configure... button?
It looks like your Renderer font size might be set very low. Have you tried resetting your Renderer font size in the Preferences window? Note, this is how the default Preferences panel, Renderer tab appears on a Mac:
and if you're font size is set to one, it looks mangled like this:
but if you click on the middle button (just down and to the right of the up and down arrows for font size selection), that will reset the font size. Then click on the blue "OK" button at the bottom right to apply the setting. If Renderer font size is your issue,
that could solve the problem.