Extending search functionality to translated fields (Mezzanine)

Question

I have been using this gist to add parallel translations to Mezzanine (version 1.4.16): https://gist.github.com/3596248

Mezzanine doesn't by default include the translated fields in searches. It looks as though it is necessary to tell Mezzanine specifically that it should include other fields whilst searching. Mezzanine's documentation on creating custom content types provides an example of this in http://mezzanine.jupo.org/docs/search-engine.html, adding the following sample lines to models.py :

objects = SearchableManager()
    search_fields = ("title", "description")

I have unsuccessfully tried variations on the lines of:

class TransRichTextPage(Translatable, RichText, Slugged):
    translation = models.ForeignKey(RichTextPage, related_name="translation")
    objects=SearchableManager()
    search_fields=("translation.title","translation.content");