SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '', 
    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 (
    5390, 5388, 5387, 5386, 5389, 5384, 5385, 
    6685, 6759, 6712, 6677, 6697, 6736, 
    6693, 6761, 6762, 6681, 6710, 6701, 
    6689, 6737, 6763, 6760, 6709
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00040

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 (5390,5388,5387,5386,5389,5384,5385,6685,6759,6712,6677,6697,6736,6693,6761,6762,6681,6710,6701,6689,6737,6763,6760,6709) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description meta_keywords meta_description search_words promo_text
5384
5385
5386
5387
5388
5389
5390
6677
6681
6685
6689
6693
6697
6701
6709
6710
6712
6736
6737
6759
6760
6761
6762
6763