"We are at the international conference."
Translation:Jesteśmy na międzynarodowej konferencji.
Simply because we don't speak like that. "W" usually implies there is some building that you can be inside, but conference is not a building, it's an event. Note that English doesn't use "in" as well.
Of course English and Polish won't correspond 100% with the preposition usage, and also there will be some exceptions to the logical rule of 'being inside'.
Thank you for the explanation. I get very confused on when to use "w" or "na". I believe this "w = inside" tip will help me a lot.
In English, if you're 'in a coference', it usually means you're a part of the event staff or a presenter or something important like that. How would that translate to Polish?
I supposed that the natural order of words in Polish is "Jesteśmy na konferencji międzynarodowej".