If general leisure events are more your thing (social events, sports) then we recommend checking out Katowice Internationals Foundation. Follow their Facebook page to receive updates on all upcoming events and general posts from the expat community.
If learning languages is more your thing, then the Language Exchange Club Katowice is right up your street. Here you can discover other people wishing to learn new languages. A free weekly meeting takes place in the city centre, organised by Multilanguage Evenings in Katowice, and includes a whole host of languages including English, Polish, French, German, Italian, Russian, and Spanish, to name a few. The meetings are free, although out of courtesy, you are encouraged to at least buy one tea/coffee/drink in the premises. Visit both Facebook profiles to find out about any upcoming events.
There are, of course, more general expat pages available on Facebook, such as Katowice Expats and Katowice Expats & Internationals for general issues and topics, but it's not uncommon to see events advertised here too. If you're an Erasmus student in the city, then the official Erasmus Facebook pages for the European Student Network in Katowice and the University of Silesia will be more than helpful.
Whether you're only staying in Katowice for the short-term, or you're in it for the long haul - we've got you covered!