Comment 3 for bug 1851668

The same here on 0.8.07.
_() function (alias of gettext module) is returning translation as strings not unicode, so when env LANGUAGE=en there is no error but if you set it to language that has accented words you have the error (e.g. 'de' or 'pl').
I fix it for me on Ubuntu 16.04 by changing duplicity/__init__.py:27 to:

    gettext.install(u'duplicity', names=[u'ngettext'], unicode=1)

and disabling OPHelpFix by changing duplicity/commandline.py:284 to:

    parser = OptionParser(option_class=DupOption, usage=usage())

Now it works for me on Python 2 and 3.