left_command -> English, right_command -> Russian

karabiner.json

{
  "rules": [
    {
      "description": "left_command -> English, right_command -> Russian",
      "manipulators": [
        {
          "conditions": [
            {
              "input_sources": [
                {
                  "language": "en"
                }
              ],
              "type": "input_source_if"
            }
          ],
          "from": {
            "key_code": "right_command"
          },
          "to": [
            {
              "key_code": "right_command"
            }
          ],
          "to_if_alone": [
            {
              "key_code": "spacebar",
              "modifiers": [
                "left_command"
              ]
            }
          ],
          "type": "basic"
        },
        {
          "conditions": [
            {
              "input_sources": [
                {
                  "language": "ru"
                }
              ],
              "type": "input_source_if"
            }
          ],
          "from": {
            "key_code": "left_command"
          },
          "to": [
            {
              "key_code": "left_command"
            }
          ],
          "to_if_alone": [
            {
              "key_code": "spacebar",
              "modifiers": [
                "left_command"
              ]
            }
          ],
          "type": "basic"
        }
      ]
    }
  ]
}