How to choose interface language for TortoiseBzr

TortoiseBzr is guessing that I want all my dialogs to be popping up in Japanese, but I do not. How can I convince it to use English?
I have my system control panel set up to use Japanese encoding for non-unicode text, but I cannot change that because various software I have installed will only show "????" everywhere if I have English set as the default codepage. There should be something in the preferences dialog that lets one change the preferred display language.