[kovidgoyal]

That's when there are no translations installed (english). Here you go:

def reverse_lookup(translated_string):
    if not hasattr(_.__self__, '_catalog'):
         return translated_string
    if not hasattr(reverse_lookup, 'cache'):
         reverse_lookup.cache = {v: k for k, v _.__self__._catalog.items()}
    ans = reverse_lookup.cache.get(translated_string, translated_string)
    if isinstance(ans, tuple):
          ans  = ans[1]
    return

this handles no translations and also plural forms. And yes the docs of gettext are useless for this, read the source of the gettext.py module instead, its pretty simple.