I can't join my friend's world

Hello!  I can't join my son's world even though he is in my friends list and I can see him online.  He also can't join me.

 Perhaps this is due to the fact that when buying the game, my account was listed as Russian (although later I changed the location to Germany after moving), and my son immediately bought the game on a new account created in Germany.

 But I would still like to figure it out.

 Thank you.