SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '' 
    OR cscart_product_descriptions.short_description IS NULL, 
    cscart_product_descriptions.full_description, 
    ''
  ) AS full_description, 
  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 (
    643, 642, 641, 645, 507, 814, 815, 218, 
    1119, 1120, 1121, 861, 859, 437, 428, 
    843, 862, 1108, 267, 857, 1749, 396, 
    1659, 791
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00110

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": 24,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (643,642,641,645,507,814,815,218,1119,1120,1121,861,859,437,428,843,862,1108,267,857,1749,396,1659,791) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description meta_keywords meta_description search_words promo_text unit_name
218
267
396
428
437
507
641
642
643
645
791
814
815
843
857
859
861
862
1108
1119
1120
1121
1659
1749