Cannot save concept

This appears to be a problem only with concepts that are not retired. This appears on this page:

• https://hostname/openmrs/dictionary/concept.form?conceptId=409

I look at an unretired concept – fine. When I save that concept, I get this error (in the pink on the top of the webpage):

Cannot save concept

Please fix all errors and try again.
You should only use locales listed among allowed locales

This server only has English (locale en), so not sure why this error message complains about French. This is the only helpful message in catalina.out:
WARN - ConceptValidator.validate(92) |2011-03-14 14:52:17,978| The locale 'fr' is not listed among allowed locales