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 (
    9839, 12702, 9841, 9848, 9840, 9844, 
    9843, 9846, 9860, 9859, 9858, 9857, 
    9852, 9861, 9862, 9847, 9863, 9856, 
    9855, 9838
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00058

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 20,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (9839,12702,9841,9848,9840,9844,9843,9846,9860,9859,9858,9857,9852,9861,9862,9847,9863,9856,9855,9838) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}