SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    23679, 23680, 23681, 23682, 23683, 23684, 
    23685, 23686, 23687, 23688, 23689, 
    23690, 23691, 23692, 23693, 23694
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00064

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 (23679,23680,23681,23682,23683,23684,23685,23686,23687,23688,23689,23690,23691,23692,23693,23694) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}