SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    10526, 10527, 10535, 10537, 10538, 10539, 
    10540, 10541, 10542, 10543, 10544, 
    10557, 10558, 10559, 10562, 10563
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00042

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 (10526,10527,10535,10537,10538,10539,10540,10541,10542,10543,10544,10557,10558,10559,10562,10563) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}