SELECT 
  pd.product_id as product_id, 
  pd.product as product, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.product, pd.product
  ) as product 
FROM 
  cscart_product_descriptions pd 
  LEFT JOIN cscart_ult_product_descriptions shared_descr ON shared_descr.product_id = pd.product_id 
  AND shared_descr.company_id = 1 
  AND shared_descr.lang_code = 'ro' 
WHERE 
  1 
  AND pd.product_id = 1129861 
  AND pd.lang_code = 'ro'

Query time 0.00040

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.00"
    },
    "nested_loop": [
      {
        "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": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "3K"
          },
          "used_columns": [
            "product_id",
            "lang_code",
            "product"
          ]
        }
      },
      {
        "table": {
          "table_name": "shared_descr",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY",
            "product_id",
            "company_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "product_id",
            "lang_code",
            "company_id"
          ],
          "key_length": "13",
          "ref": [
            "const",
            "const",
            "const"
          ],
          "rows_examined_per_scan": 0,
          "rows_produced_per_join": 1,
          "filtered": "0.00",
          "unique_row_not_found": true,
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "3K"
          },
          "used_columns": [
            "product_id",
            "lang_code",
            "company_id",
            "product"
          ]
        }
      }
    ]
  }
}

Result