SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    10766, 10767, 10768, 10776, 10781, 10789, 
    10791, 10792, 10793, 10796, 10797, 
    10801, 10806, 10807, 10812, 10815
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00032

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 (10766,10767,10768,10776,10781,10789,10791,10792,10793,10796,10797,10801,10806,10807,10812,10815) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}