SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19805, 19806, 19807, 19808, 19809, 19810, 
    19811, 19812, 19813, 19814, 19815, 
    19816, 19817, 19818, 19819, 19820
  ) 
  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 (19805,19806,19807,19808,19809,19810,19811,19812,19813,19814,19815,19816,19817,19818,19819,19820) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}