Fonts replaced with boxes

I am a first time user of GanttProject and followed the introductory video to set up my project. All was going well until I decided to customise the way my Gantt chart looked. I played around with the ‘Settings’ and made changes to the fonts. Unfortunately my screen changed from a legible one to an illegible one as all text was replaced with boxes. As a result, I am unable to read any text on the chart except for the months of the year.
Help!

If you can change the fonts back, do it and choose e.g. “Droid Sans Fallback Full H”. Otherwise, if the fonts in the whole application UI went off, you can remove the settings file to revert back to default values. The settings file is name .ganttproject and it sits in your home folder. Notice the leading dot in the file name: it might be hidden in some file browsers.

Thanks Dmitry. Appreciate your fast response and advice. All back to normal.
Cheers,
David