Babylon uses your system default fonts to display all the text in the application windows - the menus and the tool bars, the glossary and dictioanry titles, and the search results.
You can select a different font to be used for each and every langauge you use in Babylon. Your slections in this menu are saved automatically (even when the langauge lists is showing the default langauge again).
Do not forget to confirm your selections by clicking OK before closing this menu.