SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    20557, 20558, 20559, 20560, 20561, 20562, 
    20563, 20564, 20565, 20566, 20567, 
    20568, 20569, 20570, 20571, 20572
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00150

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id", "idx_product_lang"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (20557,20558,20559,20560,20561,20562,20563,20564,20565,20566,20567,20568,20569,20570,20571,20572) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}