SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    23455, 23456, 23457, 23458, 23459, 23460, 
    23461, 23462, 23463, 23464, 23465, 
    23466, 23467, 23468, 23469, 23470
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00035

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 (23455,23456,23457,23458,23459,23460,23461,23462,23463,23464,23465,23466,23467,23468,23469,23470) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}