[Karabiner-Elements] One key to change input source

change-input-sources.json

{
  "title": "Language toggler",
  "rules": [
    {
      "description": "left_shift=English, left_option=Shuangpin, right_command=Japanese, ecs=Reset_ime",
      "manipulators": [
        {
          "type": "basic",
          "from": {
            "key_code": "left_shift",
            "modifiers": {
              "optional": ["any"]
            }
          },
          "parameters": {
            "basic.to_if_held_down_threshold_milliseconds": 100
          },
          "to": [
            {
              "key_code": "left_shift",
              "lazy": true
            }
          ],
          "to_if_held_down": [
            {
              "key_code": "left_shift"
            }
          ],
          "to_if_alone": [
            {
              "select_input_source": {
                "input_source_id": "com.apple.keylayout.ABC"
              }
            }
          ]
        },
        {
          "type": "basic",
          "from": {
            "key_code": "left_option",
            "modifiers": {
              "optional": ["any"]
            }
          },
          "parameters": {
            "basic.to_if_held_down_threshold_milliseconds": 100
          },
          "to": [
            {
              "key_code": "left_option",
              "lazy": true
            }
          ],
          "to_if_held_down": [
            {
              "key_code": "left_option"
            }
          ],
          "to_if_alone": [
            {
              "select_input_source": {
                "input_mode_id": "com.apple.inputmethod.TCIM.Shuangpin",
                "input_source_id": "com.apple.inputmethod.TCIM.Shuangpin",
                "language": "zh-Hant"
              }
            }
          ]
        },
        {
          "type": "basic",
          "from": {
            "key_code": "right_command",
            "modifiers": {
              "optional": ["any"]
            }
          },
          "parameters": {
            "basic.to_if_held_down_threshold_milliseconds": 100
          },
          "to": [
            {
              "key_code": "right_command",
              "lazy": true
            }
          ],
          "to_if_held_down": [
            {
              "key_code": "right_command"
            }
          ],
          "to_if_alone": [
            {
              "select_input_source": {
                "input_mode_id": "com.apple.inputmethod.Japanese",
                "input_source_id": "com.apple.inputmethod.Kotoeri.RomajiTyping.Japanese",
                "language": "ja"
              }
            }
          ]
        },
        {
          "type": "basic",
          "from": {
            "key_code": "escape",
            "modifiers": {
              "optional": ["any"]
            }
          },
          "parameters": {
            "basic.to_if_held_down_threshold_milliseconds": 3000
          },
          "to": [
            {
              "key_code": "escape",
              "lazy": true
            }
          ],
          "to_if_held_down": [
            {
              "shell_command": "pkill -u $(whoami) -f /usr/sbin/distnoted && pkill -u $(whoami) -if input"
            }
          ]
        }
      ]
    }
  ]
}

Tips

• Use Karabiner's Event Viewer to get Input Source ID.
• Move this setting to ~/.config/karabiner/assets/complex_modifications

Reference

https://gist.github.com/noma4i/91765f432f777c690aa3bddae37cfe3e
https://ke-complex-modifications.pqrs.org/#international
https://karabiner-elements.pqrs.org/docs/json/location/