The prepositions translates differently in different contexts. It is one of the really difficult things to get correct for non native speakers. You just have to remember which goes where.
You can say drikker kaffe i en kafé for this one, and be correct. But the set phrase for going out with friends to a café and drinking coffee (and maybe something to eat) is gå på kafé hence drikker kaffe på en kafé as the preferred translation.
Takk for svaret! I actually did a bit of sleuthing myself after posting this, as I was thinking perhaps it was some remnant of Indo-European that had magically been lost in most other languages. A nice fantasy. :-) As you say, på comes from Norse (Old Norse?) opp på 'up on'. Meanwhile, it seems that Russian по comes from an earlier Indo-European root meaning something like "from" or "after", depending upon where you look, but clearly the two of them are not directly related. So it is, as you say, a coincidence, though it is somewhat eerie how similarly they are used.
Thanks again for replying! I do always enjoy your posts!