SELECT 
  p.tracking, 
  p.amount, 
  p.min_qty, 
  p.max_qty, 
  p.qty_step, 
  p.list_qty_count, 
  p.out_of_stock_actions, 
  p.product_type, 
  pd.product 
FROM 
  cscart_products AS p 
  LEFT JOIN cscart_product_descriptions AS pd ON pd.product_id = p.product_id 
  AND lang_code = 'en' 
WHERE 
  p.product_id = 391684

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.00"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "p",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.20",
            "prefix_cost": "0.00",
            "data_read_per_join": "7K"
          },
          "used_columns": [
            "product_id",
            "product_type",
            "amount",
            "tracking",
            "out_of_stock_actions",
            "min_qty",
            "max_qty",
            "qty_step",
            "list_qty_count"
          ]
        }
      },
      {
        "table": {
          "table_name": "pd",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY",
            "product_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "product_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "const",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.20",
            "prefix_cost": "0.00",
            "data_read_per_join": "6K"
          },
          "used_columns": [
            "product_id",
            "lang_code",
            "product"
          ]
        }
      }
    ]
  }
}