Ups, sorry, no, it’s not that file!
Its in the /home/user/.config/openbox (replace user for your username and note the starting dot in .config) directory, and the file is called autostart.
Something like /home/snoken/.config/openbox/autostart
That file starts all your programs (it’s run by openbox-session).
Just add the line at the end and do not forget the trailing &
setxkbmap se &
Sorry for the confusion.
Exactly the same problem here, but with Gnome 316.
Input Sources at R&L, Keyboard in Settings, cannot see “pt”
[setxkbmap pt] do the trick only for current session