The narrative web is a good example.
If you want to use specific language for a report, You have to do the following:
the_lang=self.menu.get_option_by_name(‘trans’).get_value()
self.rlocale = self.set_locale(the_lang) # The lang you want to use (i.e. fr, de_AT...)
self._ = self.rlocale.translation.sgettext
... and then you can use:
self._("Your message")