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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    21415, 11841, 10345, 20969, 20970, 8508, 
    6899, 10897
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00051

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": 8,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (21415,11841,10345,20969,20970,8508,6899,10897) and cscart_product_descriptions.lang_code = 'ru'"
        }
      }
    ]
  }
}