https://bugzilla.wikimedia.org/show_bug.cgi?id=55229
--- Comment #1 from Kunal Mehta (Legoktm) legoktm.wikipedia@gmail.com --- This message is from "category-adding" and the code for i18n.twtranslate() comes from self.site attribute which is assigned with pywikibot.getSite() by constructor. getSite() gives the site your start the bot. For commons you must run the -lang:commons -family:commons options which gives an english text by default. Since this is your own script, could you check whether your lang code isn't commons on commons site?