xonsh/docs/xonshconfig.json

{"env": {
  "EDITOR": "xo",
  "PAGER": "more"
  },
 "xontribs": ["mpl"],
 "foreign_shells": [
  {"shell": "bash",
   "login": true,
   "extra_args": ["--rcfile", "/path/to/rcfile"]
   },
  {"shell": "zsh"}
  ]
}