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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    21691, 21692, 21693, 21694, 21695, 21696, 
    21697, 21698, 21699, 21700, 21701, 
    21702, 21703, 21704, 21705, 21706, 
    21707, 21708, 21709, 21710, 21711, 
    21712, 21713, 21714
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00078

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "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 (21691,21692,21693,21694,21695,21696,21697,21698,21699,21700,21701,21702,21703,21704,21705,21706,21707,21708,21709,21710,21711,21712,21713,21714) and cscart_product_descriptions.lang_code = 'ru'"
        }
      }
    ]
  }
}

Result

product_id short_description full_description meta_keywords meta_description search_words promo_text
21691
21692
21693
21694
21695
21696
21697
21698
21699
21700
21701
21702
21703
21704
21705
21706
21707
21708
21709
21710
21711
21712
21713
21714