SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    10418, 10419, 10420, 10421, 10434, 10436, 
    10450, 10453, 10459, 10466, 10470, 
    10471, 10472, 10473, 10477, 10478
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00081

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id", "idx_product_lang"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (10418,10419,10420,10421,10434,10436,10450,10453,10459,10466,10470,10471,10472,10473,10477,10478) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}