Image filenames containing non ascii characters would be translated to a
series of underscores (____.png). To fix this, we use the unidecoe library
(which we also add to the required packages for Wagtail) which translates
each unicode character to an ascii equivalent.
For more info on how unidecode works please check @Evgeny's answer at this
question:
http://stackoverflow.com/questions/702337/how-to-make-django-slugify-work-properly-with-unicode-strings
