I got my setup working by now:
- Install pathogen (https://github.com/tpope/vim-pathogen) and vim-slime (https://github.com/jpalardy/vim-slime)
- open tmux and make a second pane (Ctrl-b + %) and open a julia REPL in it (switch back to the first after that)
- Configure vim-slime to send to the second pane of the first window (ID: 0.1) according to https://github.com/jpalardy/vim-slime#tmux
- Send your code to julia with ( 2x Ctrl + c)