SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    23711, 23712, 23713, 23714, 23715, 23716, 
    23717, 23718, 23719, 23720, 23721, 
    23722, 23723, 23724, 23725, 23726
  ) 
  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 (23711,23712,23713,23714,23715,23716,23717,23718,23719,23720,23721,23722,23723,23724,23725,23726) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}