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 (
    12546, 12633, 12573, 12548, 12580, 12565, 
    12567, 12549, 12581, 12557, 12558, 
    12570, 12568, 12547, 12569, 12584, 
    12592, 12575, 12574, 12550
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00049

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 (12546,12633,12573,12548,12580,12565,12567,12549,12581,12557,12558,12570,12568,12547,12569,12584,12592,12575,12574,12550) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}