SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    23695, 23696, 23697, 23698, 23699, 23700, 
    23701, 23702, 23703, 23704, 23705, 
    23706, 23707, 23708, 23709, 23710
  ) 
  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 (23695,23696,23697,23698,23699,23700,23701,23702,23703,23704,23705,23706,23707,23708,23709,23710) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}