def get_sites(self, domain=None, show=True, proxy=None, timeout=0):
        """
        GET Wikimedia sites via Extension:SiteMatrix
        https://www.mediawiki.org/wiki/Extension:SiteMatrix

        Optional params:
        - [domain]: filter sites on this domain, e.g. 'wiktionary.org'

        Optional arguments:
        - [show]: <bool> echo page data if true
        - [proxy]: <str> use this HTTP proxy
        - [timeout]: <int> timeout in seconds (0=wait forever)

        Data captured:
        - random: randomly selected wiki site
        - sites: <list> of wiki sites (hundreds) from commons SiteMatrix
        """
        if domain:
            self.params.update({'domain': domain})

        self.params.update({'wiki': self.COMMONS})

        self._get('sitematrix', show, proxy, timeout)

        del self.params['wiki']

        return self