SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19533, 19534, 19535, 19536, 19537, 19538, 
    19539, 19540, 19541, 19542, 19543, 
    19544, 19545, 19546, 19547, 19548
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00085

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 (19533,19534,19535,19536,19537,19538,19539,19540,19541,19542,19543,19544,19545,19546,19547,19548) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}