Postbox now supports community-translated language, including German, French, Spanish (Spain), English (British), Italian, Dutch, Portuguese (Brazilian), Russian, and Swedish, with more on the way. Note: translations may contain some English strings since they are still being worked on by volunteers.
Changing the Language
Postbox will automatically select the appropriate language based on your system locale. If you prefer to use English (or another language) instead of your system language, go to File | Languages and select your desired language. Then restart Postbox.