Did you ever launch the helper while iTunes was set to French? That's
the only way I can think of for it to get set that way.
When the audiobook helper launches, it determines the language of
iTunes by looking at the name of the "Library". In French, the
Library is called "BIBLIOTHÈQUE".
In any case, if you close both iTunes and the helper, and restart
them, the helper should be in English again (or, prompt you with an
error).
HTH,
Rob