SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    720, 724, 721, 722, 725, 723, 761, 729, 
    726, 727, 731, 732
  ) 
  AND cscart_product_descriptions.lang_code = 'fr'

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id"],
      "key": "product_id",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 12,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (720,724,721,722,725,723,761,729,726,727,731,732) and cscart_product_descriptions.lang_code = 'fr'"
    }
  }
}