SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19421, 19422, 19423, 19424, 19425, 19426, 
    19427, 19428, 19429, 19430, 19431, 
    19432, 19433, 19434, 19435, 19436
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.01112

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 (19421,19422,19423,19424,19425,19426,19427,19428,19429,19430,19431,19432,19433,19434,19435,19436) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}