Like this:
badCanonical = app.Plone.en.offering.restaurants
badCanonical.isCanonical() # False - contains a corrupted translationOf link
badCanonical.getTranslations() # Get list of what translations should exist
cat = app.Plone.reference_catalog
cat.getReferences(badCanonical, relationship="translationOf") # Displays UID referring object not existing
# Delete forward relationships
for b in cat.getReferences(badCanonical, "translationOf"): cat._deleteReference(b)
badCanonical.isCanonical() # True - fixed
badCanonical.getTranslations()
# Check that one of the translated versions still work
translated = app.Plone.sv["kalajoki-erbjuder"].restauranger
translated.isCanonical()
translated.getTranslations()