SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    10818, 10820, 10821, 10822, 10825, 10828, 
    10829, 10831, 10836, 10839, 10841, 
    10849, 10851, 10855, 10864, 10867
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00048

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 (10818,10820,10821,10822,10825,10828,10829,10831,10836,10839,10841,10849,10851,10855,10864,10867) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}