SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19853, 19854, 19855, 19856, 19857, 19858, 
    19859, 19860, 19861, 19862, 19863, 
    19864, 19865, 19866, 19867, 19868
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00061

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 (19853,19854,19855,19856,19857,19858,19859,19860,19861,19862,19863,19864,19865,19866,19867,19868) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}