karabiner.json

{
  "description": "Change to Eng, Jap, Thai by holding left_control and press left_command, right_command, right_option respectively",
  "manipulators": [
    {
      "from": {
        "key_code": "left_command",
        "modifiers": { "mandatory": ["left_control"] }
      },
      "parameters": { "basic.to_if_held_down_threshold_milliseconds": 100 },
      "to": [
        {
          "key_code": "left_command",
          "lazy": true
        }
      ],
      "to_if_alone": [{ "key_code": "japanese_eisuu" }],
      "to_if_held_down": [{ "key_code": "left_command" }],
      "type": "basic"
    },
    {
      "from": {
        "key_code": "right_command",
        "modifiers": { "mandatory": ["left_control"] }
      },
      "parameters": { "basic.to_if_held_down_threshold_milliseconds": 100 },
      "to": [
        {
          "key_code": "right_command",
          "lazy": true
        }
      ],
      "to_if_alone": [{ "key_code": "japanese_kana" }],
      "to_if_held_down": [{ "key_code": "right_command" }],
      "type": "basic"
    },
    {
      "from": {
        "key_code": "right_option",
        "modifiers": { "mandatory": ["left_control"] }
      },
      "parameters": { "basic.to_if_held_down_threshold_milliseconds": 100 },
      "to": [
        {
          "key_code": "right_option",
          "lazy": true
        }
      ],
      "to_if_alone": [
        {
          "select_input_source": {
            "input_source_id": "com.apple.keylayout.Thai"
          }
        }
      ],
      "to_if_held_down": [{ "key_code": "right_command" }],
      "type": "basic"
    }
  ]
}