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 (
    474, 426, 793, 794, 1147, 849, 850, 852, 
    853, 851, 855, 854, 856, 208, 209, 210, 
    886, 555, 630, 554, 1109, 320, 318, 319, 
    969, 970, 252, 454, 639, 49
  ) 
  AND cscart_product_descriptions.lang_code = 'ja'

Query time 0.00112

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": 30,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (474,426,793,794,1147,849,850,852,853,851,855,854,856,208,209,210,886,555,630,554,1109,320,318,319,969,970,252,454,639,49) and cscart_product_descriptions.lang_code = 'ja'"
    }
  }
}

Result

product_id short_description full_description meta_keywords meta_description search_words promo_text unit_name
49
208
209
210
252
318
319
320
426
454
474
554
555
630
639
793
794
849
850
851
852
853
854
855
856
886
969
970
1109
1147