SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19693, 19694, 19695, 19696, 19697, 19698, 
    19699, 19700, 19701, 19702, 19703, 
    19704, 19705, 19706, 19707, 19708
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00046

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 (19693,19694,19695,19696,19697,19698,19699,19700,19701,19702,19703,19704,19705,19706,19707,19708) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}