On the Language page of the Options window (accessible from the Tools, Options menu item) you can select the language of the program interface.
Accessible via Tools->Options->Language
Language
You can change the language of the program's interface by choosing another one from the drop down list. Only the languages that were installed with the program are displayed. The language of the interface changes only after the Options window is closed choosing the OK button. The selected language is kept as long as you don't change it or it becomes invalid due to software updates.
The text box below the Language field shows details about the selected language (like translator name and contact information.