SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19549, 19550, 19551, 19552, 19553, 19554, 
    19555, 19556, 19557, 19558, 19559, 
    19560, 19561, 19562, 19563, 19564
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00033

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 (19549,19550,19551,19552,19553,19554,19555,19556,19557,19558,19559,19560,19561,19562,19563,19564) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}