SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    23551, 23552, 23553, 23554, 23555, 23556, 
    23557, 23558, 23559, 23560, 23561, 
    23562, 23563, 23564, 23565, 23566
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00916

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 (23551,23552,23553,23554,23555,23556,23557,23558,23559,23560,23561,23562,23563,23564,23565,23566) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}