SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.meta_keywords, 
  cscart_product_descriptions.meta_description, 
  cscart_product_descriptions.search_words, 
  cscart_product_descriptions.promo_text, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    12504, 12505, 12506, 12507, 12508, 12509, 
    12510, 12511, 12512, 12513, 12514, 
    12515, 12516, 12517, 12518, 12519, 
    12520, 12521, 12522, 12523
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00207

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "20.21"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 20,
      "rows_produced_per_join": 20,
      "filtered": "100.00",
      "index_condition": "((`test2_gaseus`.`cscart_product_descriptions`.`product_id` in (12504,12505,12506,12507,12508,12509,12510,12511,12512,12513,12514,12515,12516,12517,12518,12519,12520,12521,12522,12523)) and (`test2_gaseus`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "18.21",
        "eval_cost": "2.00",
        "prefix_cost": "20.21",
        "data_read_per_join": "91K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "meta_keywords",
        "meta_description",
        "search_words",
        "promo_text",
        "unit_name"
      ]
    }
  }
}